Patent Publication Number: US-2023160911-A1

Title: Intestinal and fecal biomarkers for intestinal health of poultry

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. § 371 of International Patent Application PCT/EP2019/058324, filed Apr. 2, 2019, designating the United States of America and published in English as International Patent Publication WO 2019/206585 A1 on Oct. 31, 2019, which claims the benefit under Article 8 of the Patent Cooperation Treaty to European Patent Application Serial No. 18168901.9, filed Apr. 24, 2018, and to European Patent Application Serial No. 19162944.3, filed Mar. 14, 2019. 
    
    
     TECHNICAL FIELD 
     Growth performance, health and welfare of domesticated birds such as broilers heavily depends on a well-functioning intestinal tract. Consequently, there is a high need to find biomarkers that are specific for gut damage and that are easily applicable in the field. In this disclosure, a set of 20 specific proteins that can be quantified in fresh fecal droppings and intestinal content of the birds and that each specifically correlate with a damaged gut is disclosed. 
     STATEMENT ACCORDING TO 37 C.F.R. § 1.821(c) or (e)—SEQUENCE LISTING SUBMITTED AS A TXT AND PDF FILES 
     Pursuant to 37 C.F.R. § 1.821(c) or (e), files containing a TXT version and a PDF version of the Sequence Listing have been submitted concomitant with this application, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     Poultry such as broiler chickens have the lowest feed conversion of all meat-producing animals, and are, therefore, considered to be a relative sustainable source of animal protein, of which the production and consumption are still rising worldwide (Scanes, 2007; Cowieson and Selle, 2012). A well-functioning intestinal tract is of key importance for digestion and nutrient absorption and consequently low feed conversion, and is also crucial for health and welfare of broilers (Bailey et al., 2010). Indeed, intestinal diseases and syndromes are rather common in broilers and constitute the most important cause for treatment (Casewell et al., 2003). In poultry practice, coccidiosis is by far the most important intestinal disease (Yegani and Korver, 2008; Caly et al., 2015). Clinical diseases caused by bacterial pathogens are not common, but it is widely recognized that a variety of intestinal syndromes are affecting broiler performance, including subclinical necrotic enteritis and coccidiosis, viral enteritis, and various non-defined enteritis syndromes (Yegani and Korver, 2008). It is not evident to diagnose these subclinical entities and differentiate these from performance problems that have no infectious etiology, such as those caused by suboptimal formulated diets that not always cause intestinal damage. 
     The gut wall structure and morphology is a major determinant of intestinal health. Macroscopic observations of the intestinal wall at necropsy can easily be used to monitor for intestinal lesions caused by  Clostridium perfringens  and coccidia (Johnson and Reid, 1970), but are less clear for more subtle intestinal pathologies. Macroscopic alterations of the gut wall (such as gut wall tonus and thickness) and intestinal content (such as viscosity) can be used by experienced veterinarians as parameters for intestinal health but are to some extent subjective (Teirlynck et al., 2011). Histopathological microscopic observations are giving an accurate picture of intestinal health as villus structure, epithelial cell defects and inflammation can be scored (Yamauchi, 2002). In any case, the above mentioned intestinal health monitoring systems should be performed post-mortem and do not have high predictive diagnostic value, although in flocks animals can be sacrificed and used to monitor for disease. 
     Quantifiable easy-to-measure biomarkers for intestinal health are still not in use in broiler chickens in practice but would be of tremendous value as a tool to monitor for subclinical intestinal entities that cause performance problems and to evaluate control methods for intestinal health, independent of whether the triggers are derived from host, nutritional or microbial factors. Epithelial damage and epithelial permeability are likely the main drivers for intestinal health problems in broiler chickens, and damage to these cells and the gut mucosa is characterized by shortening of villi, lengthening of crypts and infiltration of inflammatory cells (Teirlynck et al., 2011; Adelman et al., 2018). It has been shown that an increase of villus length and villus-to-crypt ratio is associated with improvement of growth performance (Awad et al., 2009). While an inflammatory response in the gut is essential to control and contain infections, these responses should also have an accurate transition to an anti-inflammatory state as inflammation is costing energy that affects performance (Broom and Kogut, 2018). 
     Various systems have been developed to measure intestinal permeability, but are mainly used in experimental models (Gilani et al., 2016; Gilani et al., 2017; Wang et al., 2015). Quantification in serum or plasma of molecules that are orally administered and, because of their difference in size, can either or not cross the epithelial layer without intestinal damage and increased permeability have been shown to have value. Examples are the ratio of concentrations of lactulose and mannitol (lactulose/mannitol ratio (LMR), Gilani et al., 2017) in plasma or fluorescein isothiocyanate-dextran (FITC-dextran) in serum (Gilani et al., 2018; Kuttappan et al., 2015), after oral delivery of these compounds to the animals, with increased LMR or FITC-dextran levels indicative of high intestinal permeability. Other biomarkers for gut health have been evaluated in serum, most of them being acute phase proteins (O&#39;Reilly and Eckersall, 2014), but these are not specific for gut damage. In addition, all the blood markers need invasive sampling, what is not preferred as diagnostic test in poultry practice. While quite some markers have been identified using transcriptomic approaches on gut tissue (Hong et al., 2014), these are also not applicable in the field. There is thus clearly a need to find an intestinal and/or fecal biomarker for intestinal health of poultry that is present in fresh fecal droppings, litter or an intestinal content sample so that it is applicable in the field. In humans, calprotectin has been used to evaluate inflammation in case of severe gut diseases, and has been shown to be reliable and specific (Canani et al., 2008; Chang et al., 2014). However, for poultry such as chickens, no intestinal protein biomarkers for gut health are known. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIGS.  1 A- 1 C : Mean body weight (g) ( FIG.  1 A ), macroscopic gut appearance score ( FIG.  1   ), and coccidiosis score ( FIG.  1 C ) per pen for control and challenge on day 26. * denotes statistical significance at p&lt;0.05 between control and challenged treatment. 
         FIGS.  1 A- 1 D : Mean villus length ( FIG.  2 A ), crypt depth ( FIG.  2 B ), villus-to-crypt ratio ( FIG.  2 C ), and T-lymphocyte infiltration (CD 3  area %) per pen for control and challenge ( FIG.  2 D ) on day 26. *** denotes statistical significance at p&lt;0.0001 between control and challenge group. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure relates to a reliable, rapid and non-invasive biomarker test to diagnose gut health of poultry. With the term “poultry” is meant domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae, especially the order Galliformes, which includes chickens, quails and turkeys. The disclosure describes the identification of biomarkers that are indicative of intestinal pathology. The disclosure further describes a gut damage model in poultry wherein a set of intestinal and/or fecal biomarkers correlate with, for example, shortening of villi and CD 3  infiltration, the latter being markers for intestinal inflammation. 
     Hence, the disclosure relates, in the first instance, to a method to determine the intestinal health status of a domesticated bird comprising:
         Providing a fecal sample or an intestinal content sample obtained from the domesticated bird, and   quantifying a protein, or a fragment thereof, in the fecal sample or intestinal content sample,   wherein the protein is chosen from the group consisting of: myeloid protein 1, fibronectin, annexin A5, nucleophosmin, carbonic anhydrase 2, aminopeptidase Ey, transthyretin, ovoinhibitor, apolipoprotein A-1, hemoglobin subunit beta, superoxide dismutase [Cu—Zn], alpha-actinin-4, angiotensin-converting enzyme, WD repeat-containing protein 1, mitochondrial aspartate aminotransferase, histone H2A-IV, immunoglobulin lambda chain C region, immunoglobulin lambda chain V-1 region, cathepsin D and retinol-binding protein 4.       

     More specifically, the disclosure relates, in the first instance, to a method to determine the intestinal health status of a domesticated bird comprising:
         obtaining a fecal sample or an intestinal content sample of the domesticated bird, and   quantifying a protein, or a fragment thereof, in the fecal or intestinal content sample,   wherein the protein is chosen from the group consisting of: myeloid protein 1, fibronectin, annexin A5, nucleophosmin, carbonic anhydrase 2, aminopeptidase Ey, transthyretin, ovoinhibitor and apolipoprotein A-1.       

     The term “intestinal health status” relates, in the first instance, to the status of the gut wall structure and morphology that can be affected by, for example, infectious agents or a non-infectious cause such as a suboptimal formulated diet. The latter term thus mainly relates to epithelial damage and epithelial permeability, which is characterized by a shortening of villi, a lengthening of crypts and an infiltration of inflammatory cells. The latter damage and inflammation markers can also be associated with a “severe” macroscopic appearance of the gut, compared to a “normal” appearance, when evaluated using a scoring system such as the one described by Teirlynck et al. (2011). 
     The term “obtaining a fecal or intestinal content sample” refers to any means to collect of a fresh fecal dropping from the birds or intestinal content at necropsy of the birds. The term “intestinal content at necropsy of birds” means a sample taken from the content present in ileum or colon after the bird is euthanized. 
     The terms “quantifying a protein, or a fragment thereof, in the fecal or intestinal content sample” refers to any method known to a skilled person to quantify the proteins or fragments of in the sample. Non-limiting examples of the latter means are mass spectrometric methods (e.g., discovery and targeted proteomics, multiple reaction monitoring (MRM) assay, sequential window acquisition of all theoretical spectra assay (SWATH), . . . ), which require prior isolation of the proteins or fragments thereof from the sample. The latter isolation can be undertaken via protein extractions with different lysis buffers such as Sodium dodecyl sulfate (SDS)-based protein lysis buffer, Bacterial Protein extraction reagent (B-Per) or Urea-based lysis buffer with or without bead beating or other commonly used methods. Other non-limiting examples of means to quantify proteins or fragments thereof are ELISA and Western Blotting, which can be performed without prior protein isolation from the sample. Instead, the fecal or intestinal content sample can be diluted (10% m/v) in phosphate-buffered saline (PBS) or a 50 mM Tris, 150 mM NaCl (pH 7.2) buffer with or without bead beating prior to quantification. 
     It should be clear that the quantification of a single protein might be sufficient to determine the intestinal health status but that also a combination of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more proteins can be used to determine the intestinal health status of the poultry. 
     The protein biomarkers of the disclosure, which are indicative of intestinal pathology in poultry, are the following: 
     1. Myeloid Protein 1 
     This protein has accession number P09840 in the UniProt database (see uniprot.org/uniprot/P08940). The protein is a granule protein present in secretory granules of heterophilic granulocytes. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:1; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MPALSLIALLSLVSTAFARQWEVHPPQQQGRHWAQ 
               
               
                   
               
               
                   
                 ICSGNPFNRIRGCDRYGCGNYGASRQGKGEKHKGV 
               
               
                   
               
               
                   
                 DVICTDGSIVYAPFSGQLSGPIRFFHNGNAIDDGV 
               
               
                   
               
               
                   
                 QISGSGYCVKLVCIHPIRYHGQIQKGQQLGRMLPM 
               
               
                   
               
               
                   
                 QKVFPGIVSHIHVENCDQSDPTHLLRPIPDISPPF 
               
               
                   
               
               
                   
                 PQQDAHWAVVCAGNPTNEIRGCDKYGCGYFGAPRR 
               
               
                   
               
               
                   
                 NGKGEKHKGVDVICADGATVYAPFSGELSGPVKFF 
               
               
                   
               
               
                   
                 HNGNAIDDGVQIRGSGFCVKLLCIHPIRYNGRISK 
               
               
                   
               
               
                   
                 GQVLGRMLPMQRVFPGIISHIHVENCDRSDPTSNL 
               
               
                   
               
               
                   
                 ERGKGESEMEV 
               
            
           
         
       
     
     2. Fibronectin 
     This protein has accession number P11722 in the UniProt database (see uniprot.org/uniprot/P11722). Fibronectin (Fn) is a high molecular weight glycoprotein that consists in a soluble form in plasma and in an insoluble form as extracellular matrix (ECM) component (Pankov and Yamada, 2002). It contributes to a variety of cellular activities including wound healing. Production of fibronectin is influenced by pro-inflammatory cytokines such as IL-1-alpha, TL-6 and TNF-alpha. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:2; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 PLDQCQDSETRTFYQIGDSWEKYVHGVRYQCYCYG 
               
               
                   
               
               
                   
                 RGIGEWHCQPLQAYAPLSPPTNLRLEPNPDTGILI 
               
               
                   
               
               
                   
                 VSWDRSTTPGISGYRVTTAPTNGQQGSTLEEVVGA 
               
               
                   
               
               
                   
                 DQTSCTFENLNPGVEYNVSVYAVKDDQESIPISKT 
               
               
                   
               
               
                   
                 ITQEVPQLTDLSFVDITDSSIGLRWTPLNASTIIG 
               
               
                   
               
               
                   
                 YRITVVAAGESVPIFEDFVDSSVGYYTVTGLEPGI 
               
               
                   
               
               
                   
                 DYDISVITLINGGESAPTTLTQQTAVPPPTDLRFT 
               
               
                   
               
               
                   
                 NVGPDTMRVTWTAPTSIVLSSFLVRYSPVKKEEDV 
               
               
                   
               
               
                   
                 AELTISPSDNVVVLTNLLPGTEYLVRVYSVAEQHE 
               
               
                   
               
               
                   
                 SAPLSGIQKTGLDSPTGLDFSDITANSFTVHWIAP 
               
               
                   
               
               
                   
                 RATITGYKIRHHPEHGVGRPKEDRVPPSRNSITLT 
               
               
                   
               
               
                   
                 NLLPGTEYVVSIIAVNGREESVPLVGQQTTVSDVP 
               
               
                   
               
               
                   
                 RDLEVNPTSPTSLE1SWDAPAVTVRYYRITYGETG 
               
               
                   
               
               
                   
                 GSSPVQEFTVPGTMSRATITGLKPGVDYTITVYAV 
               
               
                   
               
               
                   
                 TGRGDSPASSKPVTVTYKTEIDTPSQMQVTDVQDN 
               
               
                   
               
               
                   
                 SISIRWLPSSSPVTGYRVTAVPKKGHGPTKTKNVP 
               
               
                   
               
               
                   
                 PDQTQVTIEGLQPTVEYMVSVYAQNQNGESLPLVE 
               
               
                   
               
               
                   
                 TAVTNIDRPKGLTFTEVDVDSIKIAWESPQGQVTR 
               
               
                   
               
               
                   
                 YRVTYSSPEDGIHELLPAPGGEEDTAELHGLRPGS 
               
               
                   
               
               
                   
                 EYTINIVAIYDDMESLPLTGTQSTAIPPPTNLKFT 
               
               
                   
               
               
                   
                 QVTPTSLTVNWNAPNVRLTGYRVRVNPKEKTGPMK 
               
               
                   
               
               
                   
                 EINLSPDSTSAVVSGLMVATKYEVSVYALKDSLTS 
               
               
                   
               
               
                   
                 RPAQGVVTTLENVSPPRRARVTDATETTITITWRT 
               
               
                   
               
               
                   
                 KTETITGFQIDAIPAASGQNPIQRTISPDVRTYTI 
               
               
                   
               
               
                   
                 TGLQPGNDYKIYLYTLNENARSSPVVIDASTAIDA 
               
               
                   
               
               
                   
                 PSNLRFLTTTTNSLLASWQPPRAKITGYIIRYDKP 
               
               
                   
               
               
                   
                 GSPAKELLPRPRPGTTEATITGLEPGTEYTIYIIA 
               
               
                   
               
               
                   
                 VKNNQKSEPLVGRKRTDDLPTLITGPHPNQPDMLD 
               
               
                   
               
               
                   
                 VPSVDEGTPYLTNNRYDNGNGIQLPGTSGHPQTIG 
               
               
                   
               
               
                   
                 HQGQQVFFEEHGYRRPVPTTATPLRPGSRRQPPNV 
               
               
                   
               
               
                   
                 DEAIEIPGYQVPIIVVPSYPHSREPRRNDTTGQEA 
               
               
                   
               
               
                   
                 LSQTTISWRPLLESTEYIISCQPVSQDEDTLQFRV 
               
               
                   
               
               
                   
                 PGTSSSATLTGLTRGATYNIIVEALKDHRRQKVLE 
               
               
                   
               
               
                   
                 EVVTVGNTVSEGLNQPADDTCYDTYTGSFYSIGEE 
               
               
                   
               
               
                   
                 WERLSETGFKLWCQCLGFGSGHFRCDSSKWCHDNG 
               
               
                   
               
               
                   
                 VNYKIGEKWDRQGENGQMIDCTCLGNGKGEF 
               
            
           
         
       
     
     3. Annexin A5 
     This protein has accession number P17153 in the UniProt database (see uniprot.org/uniprot/P17153). This protein is an anticoagulant protein that acts as an indirect inhibitor of the thromboplastin-specific complex, which is involved in the blood coagulation cascade. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:3; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAKYTRGTVTAFSPFDARADAEALRKAMKGMGTDE 
               
               
                   
               
               
                   
                 ETILKILTSRNNAQRQEIASAFKTLFGRDLVDDLK 
               
               
                   
               
               
                   
                 SELTGKFETLMVSLMRPARIFDAHALKHAIKGAGT 
               
               
                   
               
               
                   
                 NEKVLTEILASRTPAEVQNIKQVYMQEYEANLEDK 
               
               
                   
               
               
                   
                 ITGETSGHFQRLLVVLLQANRDPDGRVDEALVEKD 
               
               
                   
               
               
                   
                 AQVLFRAGELKWGTDEETFITILGTRSVSHLRRVF 
               
               
                   
               
               
                   
                 DKYMTISGFQIEETIDRETSGDLEKLLLAVVKCIR 
               
               
                   
               
               
                   
                 SVPAYFAETLYYSMKGAGTDDDTLIRVMVSRSEID 
               
               
                   
               
               
                   
                 LLDIRHEFRKNFAKSLYQMIQKDTSGDYRKALLLL 
               
               
                   
               
               
                   
                 CGGDDE 
               
            
           
         
       
     
     4. Nucleophosmin 
     This protein has accession number P16039 in the UniProt database (see uniprot.org/uniprot/P16039). Nucleophosmin is a DNA binding nuclear protein that has been described as a wound-associated protein (Mellgren, 2010). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:4; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MEDSAMDMESMGPLRPQTFLFGCELKAEKEYQFKV 
               
               
                   
               
               
                   
                 DDEENEHQLSLRTVTLGAGAKDELHVVEAEALDYE 
               
               
                   
               
               
                   
                 GNPTKVVLASLKMSVQPTVSLGGFEITPPFVLRLK 
               
               
                   
               
               
                   
                 CGSGPVYVSGQHLVALEEEPESEDEEEDTKIGNAS 
               
               
                   
               
               
                   
                 TKRPASGGGAKTPQKKPKLSEDDEDDDEDEDDDED 
               
               
                   
               
               
                   
                 DEDDLDDDEEEIKTPMKKPAREPAGKNMQKAKQNG 
               
               
                   
               
               
                   
                 KDSKPSTPASKTKTPDSKKDKSLTPKTPKVPLSLE 
               
               
                   
               
               
                   
                 EIKAKMQASVDKGCSLPKLEPKFANYVKNCFRTED 
               
               
                   
               
               
                   
                 QKVIQALWQWRQTL 
               
            
           
         
       
     
     5. Carbonic Anhydrase 2 
     This protein has accession number P07630 in the UniProt database (see uniprot.org/uniprot/P07630). This enzyme causes the rapid interconversion of carbon dioxide and water to bicarbonate and protons (or vice versa), a reaction that is important for acid/base equilibrium. The enzyme is a marker for differentiation in epithelial cells. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:5; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MSHHWGYDSHNGPAHWHEHFPIANGERQSPIAIST 
               
               
                   
               
               
                   
                 KAARYDPALKPLSFSYDAGTAKAIVNNGHSFNVEF 
               
               
                   
               
               
                   
                 DDSSDKSVLQGGALDGVYRLVQFHIHWGSCEGQGS 
               
               
                   
               
               
                   
                 EHTVDGVKYDAELHIVHWNVKYGKFAEALKHPDGL 
               
               
                   
               
               
                   
                 AVVGIFMKVGNAKPEIQKVVDALNSIQTKGKQASF 
               
               
                   
               
               
                   
                 TNFDPTGLLPPCRDYWTYPGSLTTPPLHECVIWHV 
               
               
                   
               
               
                   
                 LKEPITVSSEQMCKLRGLCFSAENEPVCRMVDNWR 
               
               
                   
               
               
                   
                 PCQPLKSREVRASFQ 
               
            
           
         
       
     
     6. Aminopeptidase Ey 
     This protein has accession number 057579 in the UniProt database (see uniprot.org/uniprot/057579). Aminopeptidase Ey (EC 3.4.11.20) from chicken ( Gallus gallus domesticus ) egg yolk is a homodimeric exopeptidase with a broad specificity for N-terminal amino acid residues at P1 position of the substrate (Midorikawa et al. 1998). Aminopeptidases are members of a membrane-bound metallopeptidase family that are expressed at a high level on the brush-border membrane of enterocytes (Gal-Garber and Uni, 2000). 
     This protein has the following amino acid sequence (i.e. SEQ IDNO:6; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAAGFFISKSVGIVGIVLALGAVATIIALSVVYAQ 
               
               
                   
               
               
                   
                 EKNKSSGGSGGSDTTSTTTASTTTTSTTTASTTAA 
               
               
                   
               
               
                   
                 PNNPWNRWRLPTALKPESYEVTLQPFLTPDDNNMY 
               
               
                   
               
               
                   
                 IFKGNSSVVFLCEEATDLILIHSNKLNYTLQGGFH 
               
               
                   
               
               
                   
                 ASLHAVNGSTPPTISNTWLETNTQYLVLQLAGPLQ 
               
               
                   
               
               
                   
                 QGQHYRLFSIFTGELADDLAGFYRSEYTEGNVTKV 
               
               
                   
               
               
                   
                 VATTQMQAPDARKAFPCFDEPAMKAVFTVTMIHPS 
               
               
                   
               
               
                   
                 DHTAISNMPVHSTYQLQMDGQSWNVTQFDPTPRMS 
               
               
                   
               
               
                   
                 TYLLAFIVSQFDYVENNTGKVQIRIWGRPAAIAEG 
               
               
                   
               
               
                   
                 QGEYALEKTGPILSFFERHYNTAYPLPKSDQVGLP 
               
               
                   
               
               
                   
                 DFNAGAMENWGLVTYRENSLLYDNAYSSIGNKERV 
               
               
                   
               
               
                   
                 VTVIAHELAHQWFGNLVTLRWWNDLWLNEGFASYV 
               
               
                   
               
               
                   
                 EYLGADSAEPTWDIKDLMVLNELYTVMATDALTTS 
               
               
                   
               
               
                   
                 HPLTFREDEINTPAQISEVFDSIAYSKGASVLRML 
               
               
                   
               
               
                   
                 SDFLTEDVFKEGLQSYLHDFSYNNTVYTDLWDHLQ 
               
               
                   
               
               
                   
                 EAVNKNSVPLPDSIGAIMDRWTLQMGFPVVTVNTL 
               
               
                   
               
               
                   
                 TGSVQQSHFLLDSNSTVERPSVFNYTWIVPITWMT 
               
               
                   
               
               
                   
                 PSRTGDRYWLVDVSATNSDFSVGSSTWLLLNLNVS 
               
               
                   
               
               
                   
                 GYFRVNYNQENWDQLLQQLSNNHQAIPVINRAQII 
               
               
                   
               
               
                   
                 DDAFNLARAQQVSVTLALNTTRFLSGETAYMPWQA 
               
               
                   
               
               
                   
                 ALNNLQYFQLMFDRSEVFGAMTKYIQKQVTPLFEY 
               
               
                   
               
               
                   
                 YRTATNNWTAIPSALMDQYNEINAISTACSYGIAE 
               
               
                   
               
               
                   
                 CQQLATALYQQWRQNVSNNPIAPNLRSAIYCSAVA 
               
               
                   
               
               
                   
                 TGGEEVWDFIWERFLEAPVVSEADKLRTALTCSTE 
               
               
                   
               
               
                   
                 TWILQRYLQYTIDPTKIRKQDATSTINSIASNVVG 
               
               
                   
               
               
                   
                 QPLAWDFIRSNWRTLFGQYGGGSFSFSRLISAVTQ 
               
               
                   
               
               
                   
                 RFNTEFELKQLEQFKADNQDIGFGSGTRALEQALE 
               
               
                   
               
               
                   
                 RTRTNINWVKENKEVVHAWFRAETASS 
               
            
           
         
       
     
     7. Transthyretin 
     This protein has accession number P27731 in the UniProt database (see uniprot.org/uniprot/P27731). Plasma transthyretin (TTR) is a plasma protein secreted by the liver that circulates bound to retinol-binding protein 4 (RBP4) and its retinol ligand. TTR is a highly conserved protein in animal species. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:7; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAFHSTLLVFLAGLVFLSEAAPLVSHGSVDSKCPL 
               
               
                   
               
               
                   
                 MVKVLDAVRGSPAANVAVKVFKKAADGTWQDFATG 
               
               
                   
               
               
                   
                 KTTEFGEIHELTTEEQFVEGVYRVEFDTSSYWKGL 
               
               
                   
               
               
                   
                 GLSPFHEYADVVFTANDSGHRHYTIAALLSPFSYS 
               
               
                   
               
               
                   
                 TTAVVSDPQE 
               
            
           
         
       
     
     The following gray boxes indicate peptides obtained via a trypsin digest of ileal samples of SEQ IDNO:7 as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample: 
     
       
         
           
               
               
            
               
                   
                 MAFHSTLLVFLAGLVFLSEAAPLVSHGSVDSKCPL 
               
               
                   
               
               
                   
                 MVKVLDAVRGSPAANVAVKFKKAADGTWQDFATGK 
               
               
                   
               
               
                   
                 TTEFGEIHELTTEEQFVEGVYRVEFDTSSYWKGLG 
               
               
                   
               
               
                   
                 LSPFHEYADVVFTANDSGHRHYTIAALLSPFSYST 
               
               
                   
               
               
                   
                 TAVVSDPQE 
               
            
           
         
       
     
     8. Ovoinhibitor 
     This protein has accession number P10184 in the UniProt database (see uniprot.org/uniprot/P10184). Ovoinhibitor is found in egg white and is a serine proteinase inhibitor that can reduce enzymatic digestion by trypsin and chymotrypsin. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:8; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MRTARQFVQVALALCCFADIAFGIEVNCSLYASGI 
               
               
                   
                   
               
               
                   
                 GKDGTSWVACPRNLKPVCGTDGSTYSNECGICLYN 
               
               
                   
                   
               
               
                   
                 REHGANVEKEYDGECRPKHVMIDCSPYLQVVRDGN 
               
               
                   
                   
               
               
                   
                 TMVACPRILKPVCGSDSFTYDNECGICAYNAEHHT 
               
               
                   
                   
               
               
                   
                 NISKLHDGECKLEIGSVDCSKYPSTVSKDGRTLVA 
               
               
                   
                   
               
               
                   
                 CPRILSPVCGTDGFTYDNECGICAHNAEQRTHVSK 
               
               
                   
                   
               
               
                   
                 KHDGKCRQEIPEIDCDQYPTRKTTGGKLLVRCPRI 
               
               
                   
                   
               
               
                   
                 LLPVCGTDGFTYDNECGICAHNAQHGTEVKKSHDG 
               
               
                   
                   
               
               
                   
                 RCKERSTPLDCTQYLSNTQNGEAITACPFILQEVC 
               
               
                   
                   
               
               
                   
                 GTDGVTYSNDCSLCAHNIELGTSVAKKHDGRCREE 
               
               
                   
                   
               
               
                   
                 VPELDCSKYKTSTLKDGRQVVACTMIYDPVCATNG 
               
               
                   
                   
               
               
                   
                 VTYASECTLCAHNLEQRTNLGKRKNGRCEEDITKE 
               
               
                   
                   
               
               
                   
                 HCREFQKVSPICTMEYVPHCGSDGVTYSNRCFFCN 
               
               
                   
                   
               
               
                   
                 AYVQSNRTLNLVSMAAC 
               
            
           
         
       
     
     9. Apolipoprotein A-1 
     This protein has accession number P08250 in the UniProt database (see uniprot.org/uniprot/P08250). Apolipoprotein (apo) A-1 is a 28 kDa exchangeable apolipoprotein that plays a key role in lipoprotein metabolism. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:9; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MRGVLVTLAVLFLTGTQARSFWQHDEPQTPLDRIR 
               
               
                   
                   
               
               
                   
                 DMVDVYLETVKASGKDAIAQFESSAVGKQLDLKLA 
               
               
                   
                   
               
               
                   
                 DNLDTLSAAAAKLREDMAPYYKEVREMWLKDTEAL 
               
               
                   
                   
               
               
                   
                 RAELTKDLEEVKEKIRPFLDQFSAKWTEELEQYRQ 
               
               
                   
                   
               
               
                   
                 RLTPVAQELKELTKQKVELMQAKLTPVAEEARDRL 
               
               
                   
                   
               
               
                   
                 RGHVEELRKNLAPYSDELRQKLSQKLEEIREKGIP 
               
               
                   
                   
               
               
                   
                 QASEYQAKVMEQLSNLREKMTPLVQEFRERLTPYA 
               
               
                   
                   
               
               
                   
                 ENLKNRLISFLDELQKSVA 
               
            
           
         
       
     
     The following gray boxes indicate peptides obtained via a trypsin digest of ileal samples of SEQ IDNO:9 as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample: 
     
       
         
           
               
               
            
               
                   
                 MRGVLVTLAVLFLTGTQARSFWQHDEPQTPLDRIR 
               
               
                   
                   
               
               
                   
                 DMVDVYLETVKASGKDAIAQFESSAVGKQLDLKLA 
               
               
                   
                   
               
               
                   
                 DNLDTLSAAAAKLREDMAPYYKEVREMWLKDTEAL 
               
               
                   
                   
               
               
                   
                 RAELTKDLEEVKEKIRPFLDQFSAKWTEELEQYRQ 
               
               
                   
                   
               
               
                   
                 RLTPVAQELKELTKQKVELMQAKLTPVAEEARDRL 
               
               
                   
                   
               
               
                   
                 RGHVEELRKNLAPYSDELRQKLSQKLEEIREKGIP 
               
               
                   
                   
               
               
                   
                 QASEYQAKVMEQLSNLREKMTPLVQEFRERLTPYA 
               
               
                   
                   
               
               
                   
                 ENLKNRLISFLDELQKSVA 
               
            
           
         
       
     
     10. Hemoglobin Subunit Beta 
     This protein has accession number P02112 in the UniProt database (see uniprot.org/uniprot/P02112). The detection of hemoglobin subunit beta (HBB) in intestinal content indicates that the administered challenges induce gut leakage and endothelial damage allowing red blood cell leakage from the blood to the lumen. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:131; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MVHWTAEEKQLITGLWGKVNVAECGAEALARLLIV 
               
               
                   
                   
               
               
                   
                 YPWTQRFFASFGNLSSPTAILGNPMVRAHGKKVLT 
               
               
                   
                   
               
               
                   
                 SFGDAVKNLDNIKNTFSQLSELHCDKLHVDPENFR 
               
               
                   
                   
               
               
                   
                 LLGDILIIVLAAHFSKDFTPECQAAWQKLVRVVAH 
               
               
                   
                   
               
               
                   
                 ALARKYH 
               
            
           
         
       
     
     11. Superoxide Dismutase 
     This protein has accession number P80566 in the UniProt database (see uniprot.org/uniprot/P80566). Superoxide dismutase (SOD) catalyzes the dismutation of superoxide radicals to hydrogen peroxide (H 2 O 2 ) and oxygen and contributes to enhanced small intestinal preservation in feline (Sun et al., 1991). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:132; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MATLKAVCVMKGDAPVEGVIHFQQQGSGPVKVTGK 
               
               
                   
                   
               
               
                   
                 ITGLSDGDHGFHVHEFGDNTNGCTSAGAHFNPEGK 
               
               
                   
                   
               
               
                   
                 QHGGPKDADRHVGDLGNVTAKGGVAEVEIEDSVIS 
               
               
                   
                   
               
               
                   
                 LTGPHCIIGRTMVVHAKSDDLGRGGDNESKLTGNA 
               
               
                   
                   
               
               
                   
                 GPRLACGVIGIAKC 
               
            
           
         
       
     
     The following gray boxes indicate peptides obtained via a trypsin digest of ileal samples of SEQ IDNO:132 as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample: 
     
       
         
           
               
               
            
               
                   
                 MATLKAVCVMKGDAPVEGVIHFQQQGSGPVKVTGK 
               
               
                   
                   
               
               
                   
                 ITGLSDGDHGFHVHEFGDNTNGCTSAGAHFNPEGK 
               
               
                   
                   
               
               
                   
                 QHGGPKDADRHVGDLGNVTAKGGVAEVEIEDSVIS 
               
               
                   
                   
               
               
                   
                 LTGPHCIIGRTMVVHAKSDDLGRGGDNESKLTGNA 
               
               
                   
                   
               
               
                   
                 GPRLACGVIGIAKC 
               
            
           
         
       
     
     12. Alpha-Actinin-4 
     This protein has accession number Q90734 in the UniProt database (see uniprot.org/uniprot/Q90734). By indirect immunofluorescence, alpha-actinin-4 (ACTN4) was shown to be localized in the apical part of chicken intestinal epithelial cells (Craig and Pardo, 1979), more specifically as a component of the tight junction (zonula occludens) (Chen et al., 2006) and/or belt desmosome (zonula adherens) (Milanini et al., 2017). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:133; the gray boxes indicate peptides obtained via a trypsin digest of colon samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MVDYHSAGQPYPYGGNGPGPNGDYMAQEDDWDRDL 
               
               
                   
                   
               
               
                   
                 LLDPAWEKQQRKTFTAWCNSHLRKAGTQIENIDED 
               
               
                   
                   
               
               
                   
                 FRDGLKLMLLLEVISGERLPKPERGKMRVHKINNV 
               
               
                   
                   
               
               
                   
                 NKALDFIASKGVNVVSIGAEEIVDGNAKMTLGMIW 
               
               
                   
                   
               
               
                   
                 TIILRFAIQDISVEETSAKEGLLLWCQRKTAPYKN 
               
               
                   
                   
               
               
                   
                 VNVQNFHISWKDGLAFNALIHRHRPELIEYDKLRK 
               
               
                   
                   
               
               
                   
                 DDPVTNLNNAFEVAEKYLDIPKMLDAEDIVNTARP 
               
               
                   
                   
               
               
                   
                 DEKAIMTYVSSFYHAFSGAQKAETAANRICKVLAV 
               
               
                   
                   
               
               
                   
                 NQENEHLMEDYEKLASDLLEWIRRTIPWLEDRSPQ 
               
               
                   
                   
               
               
                   
                 KTIQEMQQKLEDFRDYRRVHKPPKVQEKCQLEINF 
               
               
                   
                   
               
               
                   
                 NTLQTKLRLSNRPAFMPSEGRMVSDINTGWQHLEQ 
               
               
                   
                   
               
               
                   
                 AEKGYEEWLLNEIRRLEPLDHLAEKFRQKASIHEA 
               
               
                   
                   
               
               
                   
                 WTEGKEAMLKQKDYETATLSDIKALIRKHEAFESD 
               
               
                   
                   
               
               
                   
                 LAAHQDRVEQIAAIAQELNELDYYDSPSVNARCQK 
               
               
                   
                   
               
               
                   
                 ICDQWDVLGSLTHSRREALEKTEKQLETIDELHLE 
               
               
                   
                   
               
               
                   
                 YAKRAAPFNNWMESAMEDLQDMFIVHTIEEIEGLI 
               
               
                   
                   
               
               
                   
                 AAHDQFKATLPDADREREAILGIQREAQRIADLHS 
               
               
                   
                   
               
               
                   
                 IKLSGNNPYTSVTPQVINSKWERVQQLVPTRDRAL 
               
               
                   
                   
               
               
                   
                 QDEQSRQQCNERLRRQFAGQANIVGPWMQTKMEEI 
               
               
                   
                   
               
               
                   
                 GRISIEMHGTLEDQLQHLKHYEQSIVDYKPNLELL 
               
               
                   
                   
               
               
                   
                 EHEHQLVEEALIFDNKHTNYTMEHIRVGWEQLLTT 
               
               
                   
                   
               
               
                   
                 IARTINEVENQILTRDAKGISQEQMQEFRASFNHF 
               
               
                   
                   
               
               
                   
                 DKDHCGALGPEEFKACLISLGYDVENDRQGDAEFN 
               
               
                   
                   
               
               
                   
                 RIMSLVDPNGSGSVTFQAFIDFMSRETTDTDTADQ 
               
               
                   
                   
               
               
                   
                 VIASFKVLAGDKNYITAEELRRELPPEQAEYCIAR 
               
               
                   
                   
               
               
                   
                 MAPYRGPDAAPGALDYKSFSTALYGESDL 
               
            
           
         
       
     
     13. Angiotensin-Converting Enzyme 
     This protein has accession number Q10751 in the UniProt database (see uniprot.org/uniprot/Q10751). Angiotensin-converting enzyme (ACE) are localized in the intestinal brush border membrane and are involved as major functional enzymes in the final stadium of protein digestion in the small intestine (Yoshioka et al., 1987). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:134; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 AKELYGNIWSNFSDPQLKKIIGSIQTLGPSNLPLD 
               
               
                   
                   
               
               
                   
                 KRQQYNTILSDMDKIYSTAKVCLDNGTCWDLEPDI 
               
               
                   
                   
               
               
                   
                 SDIMATSRSYKKLLYAWEGWHNAAGNPLRAKYQEF 
               
               
                   
                   
               
               
                   
                 VTLSNEAYQMDGFEDTGSYWRSWYDSTTFEDDLEH 
               
               
                   
                   
               
               
                   
                 LYNQLEPLYLNLHAFVRRKLYDRYGPKYINLKGPI 
               
               
                   
                   
               
               
                   
                 PAHLLGNMWAQQWNNIYDLMVPYPDKPNLDVTNTM 
               
               
                   
                   
               
               
                   
                 VNQGWNATHMFRVSEEFFTSLGLLEMPPEFWEKSM 
               
               
                   
                   
               
               
                   
                 LEKPADGREVVCHASAWDFYNRKDFRIKQCTTVTM 
               
               
                   
                   
               
               
                   
                 EQLFTVHHEMGHVQYYLQYKDQPVSFRGGANPGFH 
               
               
                   
                   
               
               
                   
                 EAIGDVLSLSVSTPSHLQKIGLLSSAVEDEESNIN 
               
               
                   
                   
               
               
                   
                 YLLKMALEKIAFLPFGYLIDQWRWNVFSGRTPPSR 
               
               
                   
                   
               
               
                   
                 YNYDWWYLRTKYQGICAPVSRNESNFDPGAKYHIP 
               
               
                   
                   
               
               
                   
                 GNTPYIRYFVSFILQFQFHKALCQAANHTGPLHTC 
               
               
                   
                   
               
               
                   
                 DIYMSKEAGAKLREVLKAGSSKSWQEILFNLTGTD 
               
               
                   
                   
               
               
                   
                 KMDAGALLEYFSPVTTWLQEQNNKTNEVLGWPEFD 
               
               
                   
                   
               
               
                   
                 WRSPIPEGYPEGIDKIVDEAQAKEFLSEYNSTAEV 
               
               
                   
                   
               
               
                   
                 VWNAYTEASWEYNTNITDHNKEVMLEKNLAMSKHT 
               
               
                   
                   
               
               
                   
                 IEYGMRARQFDPSDFQDETVTRILNKLSVLERAAL 
               
               
                   
                   
               
               
                   
                 PEDELKEYNTLLSDMETTYSVAKVCRENNTFHPLD 
               
               
                   
                   
               
               
                   
                 PDLTDILATSRDYNELLFAWKGWWDASGAKIKDKY 
               
               
                   
                   
               
               
                   
                 KRYVELSNKAAVLNGYTDNGAYWRSLYETPTFEED 
               
               
                   
                   
               
               
                   
                 LERLYLQLQPLYLNLHAYVRRALYNKYGAEHISLK 
               
               
                   
                   
               
               
                   
                 GPIPAHLLGNMWAQSWSNIFDLVMPFPDATKVDAT 
               
               
                   
                   
               
               
                   
                 PAMKQQGWTPKMMFEESDRFFTSLGLIPMPQEFWD 
               
               
                   
                   
               
               
                   
                 KSMIEKPADGREVVCHASAWDFYNRKDFRIKQCTV 
               
               
                   
                   
               
               
                   
                 VNMDDLITVHHEMGHVQYFLQYMDQPISFRDGANP 
               
               
                   
                   
               
               
                   
                 GFHEAIGDVMALSVSTPKHLHSINLLDQVTENEES 
               
               
                   
                   
               
               
                   
                 DINYLMSIALDKIAFLPFGYLMDQWRWKVFDGRIK 
               
               
                   
                   
               
               
                   
                 EDEYNQQWWNLRLKYQGLCPPVPRSEDDFDPGAKF 
               
               
                   
                   
               
               
                   
                 HIPANVPYIRYFVSFVIQFQFHQALCKAAGHTGPL 
               
               
                   
                   
               
               
                   
                 HTCDIYQSKEAGKLLGDAMKLGFSKPWPEAMQLIT 
               
               
                   
                   
               
               
                   
                 GQPNMSAEALMSYFEPLMTWLVKKNTENGEVLGWP 
               
               
                   
                   
               
               
                   
                 EYSWTPYAVTEFHAATDTADFLGMSVGTKQATAGA 
               
               
                   
                   
               
               
                   
                 WVLLALALVFLITSIFLGVKLFSSRRKAFKSSSEM 
               
               
                   
                   
               
               
                   
                 ELK 
               
            
           
         
       
     
     14. WD Repeat-Containing Protein 1 
     This protein has accession number 093277 in the UniProt database (see uniprot.org/uniprot/093277). WD (tryptophan-aspartate) repeat-containing protein 1 (WDR1), also called actin-interacting protein 1 (AIP1), acts as a cofactor of ADF-cofilin and facilitates actin turnover by disassembly of actin filaments (Fujibuchi et al., 2004). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:135; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MRMPYEIKKVFASLPQVERGVSKIIGGDPKGNNFL 
               
               
                   
                   
               
               
                   
                 YTNGKCVVIRNIDNPAIADIYTEHAHQVVVAKYAP 
               
               
                   
                   
               
               
                   
                 SGFYIASGDVSGKLRIWDTTQKEHLLKYEYQPFAG 
               
               
                   
                   
               
               
                   
                 KIKDLAWTEDSKRIAVVGEGREKFGAVFLWDSGSS 
               
               
                   
                   
               
               
                   
                 VGEITGHNKVINSVDIKQTRPYRLATGSDDNCAAF 
               
               
                   
                   
               
               
                   
                 FEGPPFKFKFTLSDHTRFVNCVRFSPDGNRFATAS 
               
               
                   
                   
               
               
                   
                 ADGQIFIYDGKTGEKVCALGGGKAHDGGIYAISWS 
               
               
                   
                   
               
               
                   
                 PDSSQLLSASGDKTAKIWDVGANSVVSTFNMGSNV 
               
               
                   
                   
               
               
                   
                 LDQQLGCLWQKDHLLSLSLSGYINYLDKNNPDKPL 
               
               
                   
                   
               
               
                   
                 RVIKGHSKSIQCLTVHKNGGKSYIYSGSNDGHINY 
               
               
                   
                   
               
               
                   
                 WDSDTGENDGFSGKGHTNQVSRMAVDEMDQLVTCS 
               
               
                   
                   
               
               
                   
                 MDDTVRYTNLSKRDYSGQDAVKMDVQPKCLAVGPG 
               
               
                   
                   
               
               
                   
                 GYTVVLCIGQIVLMKDKKKCFAIDDLGYEPEAVAV 
               
               
                   
                   
               
               
                   
                 HPGGGSVAVGGTDGNVRLYSIQGTSLKSDDKTLEA 
               
               
                   
                   
               
               
                   
                 KGPVTDLAYSHDGAFLAVCDANKVVTVFSVPDGYV 
               
               
                   
                   
               
               
                   
                 EHNVFYGHHAKVVCIAWSPDNEHFASGGMDMMVYV 
               
               
                   
                   
               
               
                   
                 WTVSDPETRIKIPDAHRLHHVSGLAWLDEHTLVTT 
               
               
                   
                   
               
               
                   
                 SHDASVKEWSISYN 
               
            
           
         
       
     
     15. Aspartate Aminotransferase, Mitochondrial 
     This protein has accession number P00508 in the UniProt database (see uniprot.org/uniprot/P00508). Aspartate aminotransferase, mitochondrial (AATM), formerly known as glutamic-oxaloacetic transaminase, catalyzes the reaction of L-aspartate and 2-oxoglutatarate to oxaloacetate and glutamate. This mitochondrial isotype is present predominantly in liver (Kaneko et al., 2008). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:136; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MALLQSRLLLSAPRRAAATARASSWWSHVEMGPPD 
               
               
                   
                   
               
               
                   
                 PILGVTEAFKRDTNSKKMNLGVGAYRDDNGKSYVL 
               
               
                   
                   
               
               
                   
                 NCVRKAEAMIAAKKMDKEYLPIAGLADFTRASAEL 
               
               
                   
                   
               
               
                   
                 ALGENSEAFKSGRYVTVQGISGTGSLRVGANFLQR 
               
               
                   
                   
               
               
                   
                 FFKFSRDVYLPKPSWGNHTPIFRDAGLQLQAYRYY 
               
               
                   
                   
               
               
                   
                 DPKTCSLDFTGAMEDISKIPEKSIILLHACAHNPT 
               
               
                   
                   
               
               
                   
                 GVDPRQEQWKELASVVKKRNLLAYFDMAYQGFASG 
               
               
                   
                   
               
               
                   
                 DINRDAWALRHFIEQGIDVVLSQSYAKNMGLYGER 
               
               
                   
                   
               
               
                   
                 AGAFTVICRDAEEAKRVESQLKILIRPMYSNPPMN 
               
               
                   
                   
               
               
                   
                 GARIASLILNTPELRKEWLVEVKGMADRIISMRTQ 
               
               
                   
                   
               
               
                   
                 LVSNLKKEGSSHNWQHITDQIGMFCFTGLKPEQVE 
               
               
                   
                   
               
               
                   
                 RLTKEFSIYMTKDGRISVAGVASSNVGYLAHAIHQ 
               
               
                   
                   
               
               
                   
                 VTK 
               
            
           
         
       
     
     16. Histone H2A-IV 
     This protein has accession number P02263 in the UniProt database (see uniprot.org/uniprot/P02263). H2A4 is a core component of nucleosomes that wrap and compact DNA into chromatin. 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:137; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MSGRGKQGGKARAKAKSRSSRAGLQFPVGRVHRLL 
               
               
                   
                   
               
               
                   
                 RKGNYAERVGAGAPVYLAAVLEYLTAEILELAGNA 
               
               
                   
                   
               
               
                   
                 ARDNKKTRIIPRHLQLAIRNDEELNKLLGKVTIAQ 
               
               
                   
                   
               
               
                   
                 GGVLPNIQAVLLPKKTDSHKAKAK 
               
            
           
         
       
     
     17. Ig Lambda Chain C Region 
     This protein has accession number P20763 in the UniProt database (see uniprot.org/uniprot/P20763). Antibodies consist of two heavy and light chains whereby birds only have one isotope of light chain, namely lambda (λ). The light chain is made up by a constant, Ig lambda chain C-region (LAC), and a variable region, Ig lambda chain V1-region (LV1) (Benčina et al., 2014). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:138; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 QPKVAPTITLFPPSKEELNEATKATLVCLINDFYP 
               
               
                   
                   
               
               
                   
                 SPVTVDWVIDGSTRSGETTAPQRQSNSQYMASSYL 
               
               
                   
                   
               
               
                   
                 SLSASDWSSHETYTCRVTHNGTSITKTLKRSEC 
               
            
           
         
       
     
     18. Ig Lambda Chain V1 Region 
     This protein has accession number P04210 in the UniProt database (see uniprot.org/uniprot/P04210). Antibodies consist of two heavy and light chains whereby birds only have one isotope of light chain, namely lambda (λ). The light chain is made up by a constant, Ig lambda chain C-region (LAC), and a variable region, Ig lambda chain V1-region (LV1) (Benčina et al., 2014). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:139; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAWAPLLLAVLAHTSGSLVQAALTQPSSVSANPGE 
               
               
                   
                   
               
               
                   
                 TVKITCSGDRSYYGWYQQKAPGSAPVTLIYDNTNR 
               
               
                   
                   
               
               
                   
                 PSNIPSRFSGSKSGSTATLTITGVQADDEAVYYCG 
               
               
                   
                   
               
               
                   
                 SADSSSTA 
               
            
           
         
       
     
     19. Cathepsin D 
     This protein has accession number Q05744 in the UniProt database (see uniprot.org/uniprot/Q05744). Cathepsin D (CATD), an aspartic proteinase, is optimally active against denatured proteins at acidic pH. CATD is expressed in lysozomes, but also exists bound to some intracellular membranes, which has been detected in several different cell types (Fusek and Vetvicka, 1995). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:140; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAPRGLLVLLLLALVGPCAALIRIPLTKFTSTRRM 
               
               
                   
                   
               
               
                   
                 LTEVGSEIPDMNAITQFLKFKLGFADLAEPTPEIL 
               
               
                   
                   
               
               
                   
                 KNYMDAQYYGEIGIGTPPQKFTVVFDTGSSNLWVP 
               
               
                   
                   
               
               
                   
                 SVHCHLLDIACLLHHKYDASKSSTYVENGTEFAIH 
               
               
                   
                   
               
               
                   
                 YGTGSLSGFLSQDTVTLGNLKIKNQIFGEAVKQPG 
               
               
                   
                   
               
               
                   
                 ITFIAAKFDGILGMAFPRISVDKVTPFFDNVMQQK 
               
               
                   
                   
               
               
                   
                 LIEKNIFSFYLNRDPTAQPGGELLLGGTDPKYYSG 
               
               
                   
                   
               
               
                   
                 DFSWVNVTRKAYWQVHMDSVDVANGLTLCKGGCEA 
               
               
                   
                   
               
               
                   
                 IVDTGTSLITGPTKEVKELQTAIGAKPLIKGQYVI 
               
               
                   
                   
               
               
                   
                 SCDKISSLPVVTLMLGGKPYQLTGEQYVFKVSAQG 
               
               
                   
                   
               
               
                   
                 ETICLSGFSGLDVPPPGGPLWILGDVFIGPYYTVF 
               
               
                   
                   
               
               
                   
                 DRDNDSVGFAKCV 
               
            
           
         
       
     
     20. Retinol-Binding Protein 4 
     This protein has accession number P41263 in the UniProt database (see uniprot.org/uniprot/P41263). Transthyretin (TTR) is a highly conserved protein in animal species that is involved in transport of thyroid hormones and retinol bound to retinol-binding protein 4 (RET4) in the bloodstream (Ingenbleek &amp; Bernstein, 2015). Retinol (vitamin A) is known to be essential for differentiation and proliferation of epithelial cells (Thomas et al., 2004). 
     This protein has the following amino acid sequence (i.e., SEQ IDNO:141; the gray boxes indicate peptides obtained via a trypsin digest of ileal samples as is described further and represent non-limiting examples of protein fragments that can be quantified in a fecal or an intestinal content sample): 
     
       
         
           
               
               
            
               
                   
                 MAYTWRALLLLALAFLGSSMAERDCRVSSFKVKEN 
               
               
                   
                   
               
               
                   
                 FDKNRYSGTWYAMAKKDPEGLFLQDNVVAQFTVDE 
               
               
                   
                   
               
               
                   
                 NGQMSATAKGRVRLFNNWDVCADMIGSFTDTEDPA 
               
               
                   
                   
               
               
                   
                 KFKMKYWGVASFLQKGNDDHWVVDTDYDTYALHYS 
               
               
                   
                   
               
               
                   
                 CRELNEDGTCADSYSFVFSRDPKGLPPEAQKIVRQ 
               
               
                   
                   
               
               
                   
                 RQIDLCLDRKYRVIVHNGFCS 
               
            
           
         
       
     
     The disclosure further relates to a method as described above wherein an increased level of a protein chosen from the group consisting of myeloid protein 1, fibronectin, annexin A5, nucleophosmin, carbonic anhydrase 2, transthyretin, ovoinhibitor, apolipoprotein A-1, hemoglobin subunit beta, alpha-actinin-4, histone H2A-IV and retinol-binding protein 4 present in the fecal or intestinal content sample, when compared to the level found in fecal and/or intestinal content samples of healthy control animals, is an indicator of poor intestinal health. The terms “increased levels of protein compared to the level found in healthy control animals” means at least a two-fold increase such as a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold . . . increase compared to the level found in healthy control animals. 
     The disclosure further relates to a method as described above wherein a decreased level of the protein aminopeptidase Ey, superoxide dismutase [Cu—Zn], angiotensin-converting enzyme, WD repeat-containing protein 1, mitochondrial aspartate aminotransferase, immunoglobulin lambda chain C region, immunoglobulin lambda chain V-1 region and cathepsin D present in the fecal or an intestinal content sample, when compared to the level found in fecal and/or an intestinal content samples of healthy control animals, is an indicator of poor intestinal health. The terms “decreased levels of protein compared to the level found in healthy control animals” means at least a two-fold decrease such as a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold . . . decrease compared to the level found in healthy control animals. 
     The disclosure thus relates to a method as described above wherein the protein abundance is significantly differential between healthy and challenged group and/or level of protein correlates with the intestinal health as determined by measuring villus length in the duodenum of the birds, and/or, by measuring villus-to-crypt ratio in the duodenum of the birds, and/or by measuring T-lymphocyte infiltration is the villi, and/or, by scoring the macroscopic gut appearance of the birds. It is clear that the intestinal health is a measure for/correlates with performance parameters of the birds such as body weight and feed conversion ratio. 
     The disclosure further relates to a method as described above wherein the intestinal content sample is a colonic content sample and wherein the protein is chosen from the group consisting of: myeloid protein 1, fibronectin, annexin A5, nucleophosmin, carbonic anhydrase 2, aminopeptidase Ey, transthyretin, ovoinhibitor, apolipoprotein A-1, hemoglobin subunit beta, superoxide dismutase [Cu—Zn] and alpha-actinin-4. 
     The disclosure further relates to a method as described above wherein the intestinal content sample is an ileal content sample and wherein the protein is chosen from the group consisting of: aminopeptidase Ey, transthyretin, apolipoprotein A-1, superoxide dismutase [Cu—Zn], angiotensin-converting enzyme, WD repeat-containing protein 1, mitochondrial aspartate aminotransferase, histone H2A-IV, immunoglobulin lambda chain C region, immunoglobulin lambda chain V-1 region, cathepsin D and retinol-binding protein 4. 
     More specifically, the disclosure relates to a method as described above wherein the fragment of myeloid protein 1 comprises at least one of the following amino acid sequences: APFSGELSGPVK (SEQ IDNO:10), APFSGQLSGPIR (SEQ IDNO:11), FSGELSGPVK (SEQ IDNO:12), HGQIQK (SEQ IDNO:13), SDPTSNLER (SEQ IDNO:14), SGELSGPVK (SEQ IDNO:15), SGQLSGPIR (SEQ IDNO:16), VFPGIISHI (SEQ IDNO:17), VFPGIVSH (SEQ IDNO:18), VFPGIVSHI (SEQ IDNO:19); wherein the fragment of fibronectin comprises at least one of the following amino acid sequences: ATITGYK (SEQ IDNO:20), DDQESIPISK (SEQ IDNO:21); wherein the fragment of annexin A5 comprises at least one of the following amino acid sequences: KAMKGMGTDEETILK (SEQ IDNO:22), LLLAVVK (SEQ IDNO:23), VDEALVEK (SEQ IDNO:24); wherein the fragment of nucleophosmin comprises at least one of the following amino acid sequences: IGNASTK (SEQ IDNO:25), TPDSK (SEQ IDNO:26), TVTLGAGAK (SEQ IDNO:27), VVLASLK (SEQ IDNO:28); wherein the fragment of carbonic anhydrase 2 comprises at least one of the following amino acid sequences: VGNAKPEIQK (SEQ IDNO:29), VVDALNSIQTK (SEQ IDNO:30); wherein the fragment of aminopeptidase Ey comprises at least one of the following amino acid sequences: ADNQDIGFGSGTR (SEQ IDNO:31), AIAEGQGEYALEK (SEQ IDNO:32), APVVSEADK (SEQ IDNO:33), AQIIDDAFNLAR (SEQ IDNO:34), AVFTVTMIHPS (SEQ IDNO:35), AWDFIR (SEQ IDNO:36), DFIWER (SEQ IDNO:37), DFLTEDVFK (SEQ IDNO:38), DHLQEAVNK (SEQ IDNO:39), DLWDHLQEAVNK (SEQ IDNO:40), DNAYSSIGNK (SEQ IDNO:41), EAPVVSEADK (SEQ IDNO:42), EGQGEYALEK (SEQ IDNO:43), ENSLLYDNAYSSIGNK (SEQ IDNO:44), EQALER (SEQ IDNO:45), FLEAPVVSEADK (SEQ IDNO:46), FLEAPVVSEADKLR (SEQ IDNO:47), FNTEFELK (SEQ IDNO:48), GADSAETWDIK (SEQ IDNO:49), HYNTAYPLPK (SEQ IDNO:50), IAEGQGEYALEK (SEQ IDNO:51), ILSFFER (SEQ IDNO:52), IWGRPAAIAE (SEQ IDNO:53), IWGRPAAIAEGQGEY (SEQ IDNO:54), IWGRPAAIAEGQGEYALEK (SEQ IDNO:55), KQDATSTIN (SEQ IDNO:56) KQDATSTINSIASNVVGQPL (SEQ IDNO:57), KQDATSINSIASNVVGQPLA (SEQ IDNO:58), LAGPLQQGQHYR (SEQ IDNO:59), LEAPVVSEADK (SEQ IDNO:60), LPTALKPESYEVTLQPF (SEQ IDNO:61), MLSDFLTEDVFK (SEQ IDNO:62), NSVPLPDSIGAIMDR (SEQ IDNO:63), PAAIAEGQGEYALEK (SEQ IDNO:64), QAIPVINR (SEQ IDNO:65), QDATSTINSIASNVVGQPL (SEQ IDNO:66), QNVSNNPIAPNLR (SEQ IDNO:67), SDFLTEDVFK (SEQ IDNO:68), SDQVGLPDFNAGAMENWG (SEQ IDNO:69), SEVFDSIAYSK (SEQ IDNO:70), SLLYDNAYSSIGNK (SEQ IDNO:71), SNNHQAIPVINR (SEQ IDNO:72), SVPLPDSIGAIMDR (SEQ IDNO:73), TDLWDHLQEAVNK (SEQ IDNO:74), TGELADDLAGFYR (SEQ IDNO:75), TGPILSFFER (SEQ IDNO:76), TIDPTK (SEQ IDNO:77), TLFGQYGGGSFSFSR (SEQ IDNO:78), TNINWVK (SEQ IDNO:79), VNYNQENWDQLL (SEQ IDNO:80), VNYQENWDQLLQ (SEQ IDNO:81), VNYQENWDQLLQQ (SEQ IDNO:82), VVATTQMQAPDAR (SEQ IDNO:83), WRLPTAL (SEQ IDNO:84), WRLPTALKPES (SEQ IDNO:85), WRLPTALKPESYEVTLQPF (SEQ IDNO:86), YDNAYSSIGNK (SEQ IDNO:87), YLQYTIDPTK (SEQ IDNO:88), YPLPK (SEQ IDNO:89); wherein the fragment of transthyretin comprises at least one of the following amino acid sequences: AADGTWQDFATGK (SEQ IDNO:90), CPLMVK (SEQ IDNO:91), DGTWQDFATGK (SEQ IDNO:92), DVVFTANDSGHR (SEQ IDNO:93), GLGLSPFH (SEQ IDNO:94), GLGLSPFHEY (SEQ IDNO:95), GLGLSPFHEYA (SEQ IDNO:96), GLGLSPFHEYADVVF (SEQ IDNO:97), GLGLSPFHEYADVVFTANDSGHR (SEQ IDNO:98), GSPAANVAVK (SEQ IDNO:99), GSPAANVAVKV (SEQ IDNO:100), GTWQDFATGK (SEQ IDNO:101), HYTIAALL (SEQ IDNO:102), HYTIAALLSPF (SEQ IDNO:103), HYTIAALLSPFS (SEQ IDNO:104), TTEEQFVEGVYR (SEQ IDNO:105), TTEFGEIHEL (SEQ IDNO:106), TTEFGEIHELTTEEQ (SEQ IDNO:107), TTEFGEIHELTTEEQFVEGV (SEQ IDNO:108), TTEFGEIHELTTEEQFVEGVYR (SEQ IDNO:109), TTEFGEIHELTTEEQFVEGVYRVEFDTSSYWK (SEQ IDNO:110), VEFDTSSYWK (SEQ IDNO:111), VLDAVR (SEQ IDNO:112); wherein the fragment of ovoinhibitor comprises at least one of the following amino acid sequences: EHGANVEK (SEQ IDNO:113), TLNLVSMAAC (SEQ IDNO:114), TLVACPR (SEQ IDNO:115); wherein the fragment of apolipoprotein A-1 comprises at least one of the following amino acid sequences: DLEEVKEK (SEQ IDNO:116), EMWLK (SEQ IDNO:117), IRDMVDV (SEQ IDNO:118), IRPFLDQF (SEQ IDNO:119), IRPFLDQFSAK (SEQ IDNO:120), LADNLDTLSAAAAK (SEQ IDNO:121), LISFLDELQK (SEQ IDNO:122), LSQKLEEI (SEQ IDNO:123), LTPVAEEAR (SEQ IDNO:124), LTPVAQELK (SEQ IDNO:125), LTPYAENLK (SEQ IDNO:126), MTPLVQEFR (SEQ IDNO:127), QKLSQK (SEQ IDNO:128), QLDLK (SEQ IDNO:129), YKEVR (SEQ IDNO:130); wherein the fragment of hemoglobin subunit beta comprises at least one of the following amino acid sequences: KVLTSFGDAV (SEQ IDNO:142), LHVDPENF (SEQ IDNO:143), LLIVYPWTQR (SEQ IDNO:144), NLDNIK (SEQ IDNO:145), VLTSFGDAVK (SEQ IDNO:146); wherein the fragment of superoxide dismutase [Cu—Zn]comprises at least one of the following amino acid sequences: AVCVMK (SEQ IDNO:147), FQQQGSGPVK (SEQ IDNO:148), GDAPVEGVIHFQQQGSGPVK (SEQ IDNO:149), GGVAEVEI (SEQ IDNO:150), GGVAEVEIEDSVISLTGPH (SEQ IDNO:151), GVIGIAK (SEQ IDNO:152), HVGDLGNVTA (SEQ IDNO:153), HVGDLGNVTAK (SEQ IDNO:154), ITGLSDGDHGFHVH (SEQ IDNO:155), LACGVIGIAK (SEQ IDNO:156), LTGNAGPR (SEQ IDNO:157), SDDLGR (SEQ IDNO:158), SDDLGRGGDNESK (SEQ IDNO:159), TMVVHA (SEQ IDNO:160); wherein the fragment of alpha-actinin-4 comprises at least one of the following amino acid sequences: DAEDIVNTARDPEK (SEQ IDNO:161), TIPWLEDR (SEQ IDNO:162); wherein the fragment of angiotensin-converting enzyme comprises at least one of the following amino acid sequences: AALPEDELKEYNTLLSDMETTYSVAK (SEQ IDNO:163), ALYNK (SEQ IDNO:164), DGANPGFHEAIGDV (SEQ IDNO:165), DGANPGFHEAIGDVMA (SEQ IDNO:166), DGANPGFHEAIGDVMAL (SEQ IDNO:167), DYNELLFAWK (SEQ IDNO:168), ETPTFEEDLER (SEQ IDNO:169), EVMLEK (SEQ IDNO:170), FEESDR (SEQ IDNO:171), FFTSLGLIPMPQEFWDK (SEQ IDNO:172), GGANPGFHEAIGDVLS (SEQ IDNO:173), GLIPMPQEFWDK (SEQ IDNO:174), GLLEMPPEFWEK (SEQ IDNO:175), GPIPAHL (SEQ IDNO:176), GPIPAHLLGNMW (SEQ IDNO:177), GPIPAHLLGNMWAQQ (SEQ IDNO:178), GPIPAHLLGNMWAQS (SEQ IDNO:179), GYLIDQWR (SEQ IDNO:180), IIGSIQTLGPSNLPLDK (SEQ IDNO:181), IIGSIQTLGPSNLPLDKR (SEQ IDNO:182), IKEDEYNQQWWNL (SEQ IDNO:183), IYSTAK (SEQ IDNO:184), KIIGSIQTLGPSNLPLDK (SEQ IDNO:185), LLGDAMK (SEQ IDNO:186), LLYAWEGWHNAAGNPLR (SEQ IDNO:187), LSVLER (SEQ IDNO:188), MSIALDK (SEQ IDNO:189), NTILSDMDK (SEQ IDNO:190), QCTVVNMDDLITVH (SEQ IDNO:191), QFDPSDFQDETVTR (SEQ IDNO:192), QQGWTPK (SEQ IDNO:193), QQYNTILSDMDK (SEQ IDNO:194), RYVELSNK (SEQ IDNO:195), SLGLIPMPQEFWDK (SEQ IDNO:196), SLSVSTPSHLQK (SEQ IDNO:197), SLYETPTFEEDLER (SEQ IDNO:198), SMIEKPADGR (SEQ IDNO:199), SNIFDLVMPFPDATK (SEQ IDNO:200), SVSTPK (SEQ IDNO:201), SVSTPSHLQK (SEQ IDNO:202), TLGPSNLPLDK (SEQ IDNO:203), TNEVLGWPEFDWRSPIPEGYPEGIDK (SEQ IDNO:204), TSLGLIPMPQEFWDK (SEQ IDNO:205), TSLGLLEMPPEFWEK (SEQ IDNO:206), VDATPAMK (SEQ IDNO:207), VELSNK (SEQ IDNO:208), YGAEHISLK (SEQ IDNO:209), YHIPGNTPY (SEQ IDNO:210), YINLK (SEQ IDNO:211), YNELLFAWK (SEQ IDNO:212), YQGLCPPVPR (SEQ IDNO:213), YVELSNK (SEQ IDNO:214); wherein the fragment of WD repeat-containing protein 1 comprises at least one of the following amino acid sequences: IIGGDPK (SEQ IDNO:215), KVFASLPQVERGVSK (SEQ IDNO:216), VINSVDIK (SEQ IDNO:217); wherein the fragment of mitochondrial aspartate aminotransferase comprises at least one of the following amino acid sequences: GPPDPILGVTEAFK (SEQ IDNO:218), LLLSAPR (SEQ IDNO:219), MDKEYLPI (SEQ IDNO:220), MGLYGER (SEQ IDNO:221), NPTGVDPR (SEQ IDNO:222), TQLVSNLK (SEQ IDNO:223); wherein the fragment of histone H2A-IV comprises at least one of the following amino acid sequences: NDEELNK (SEQ IDNO:224), VTIAQGGVLPNIQAAVLLPK (SEQ IDNO:225); wherein the fragment of immunoglobulin lambda chain C region comprises at least one of the following amino acid sequences: DFYPSPVTVDWVIDGSTR (SEQ IDNO:226), ITLFPPSK (SEQ IDNO:227), NDFYPSPVTVDWVIDGSTR (SEQ IDNO:228), SGETTAPQR (SEQ IDNO:229), THNGTSITK (SEQ IDNO:230), TVDWVIDGSTR (SEQ IDNO:231), VAPTITLFPPSK (SEQ IDNO:232), VAPTITLFPPSKEELN (SEQ IDNO:233), VAPTITLFPPSKEELNEAT (SEQ IDNO:234), VAPTITLFPPSKEELNEATK (SEQ IDNO:235), VTHNGTSITK (SEQ IDNO:236); wherein the fragment of immunoglobulin lambda chain V1 region comprises at least one of the following amino acid sequences: ALTQPSSVSANPGETVK (SEQ IDNO:237), APGSAPVTLIYDNTNRPSNIPSR (SEQ IDNO:238), GSAPVTLIYDNTNRPSNIPSR (SEQ IDNO:239), ITCSGDR (SEQ IDNO:240), NPGETVK (SEQ IDNO:241), PSNIPSR (SEQ IDNO:242), RPSNIPSR (SEQ IDNO:243), SANPGETVK (SEQ IDNO:244), SVSANPGETVK (SEQ IDNO:245), YGWYQQK (SEQ IDNO:246); wherein the fragment of cathepsin D comprises at least one of the following amino acid sequences: DPTAQPGGELLLGGTDPK (SEQ IDNO:247), ELQTAIGAKPL (SEQ IDNO:248), ELQTAIGAKPLI (SEQ IDNO:249), FDGILGMAFPR (SEQ IDNO:250), IPLTK (SEQ IDNO:251), QPGGELLLGGTDPK (SEQ IDNO:252), VTPFFDNVMQQK (SEQ IDNO:253); wherein the fragment of retinol-binding protein 4 comprises at least one of the following amino acid sequences: QIDLCLDR (SEQ IDNO:254), TVDENGQMSATAK (SEQ IDNO:255). 
     Furthermore, the disclosure relates to a method as described above wherein the domesticated bird is a broiler. The term “broiler” refers to any chicken ( Gallus gallus domesticus ) that is bred and raised specifically for meat production. 
     Moreover, the preset disclosure relates to a method as described above wherein the proteins or fragments thereof are quantified by using antibodies that specifically bind to the proteins or fragments thereof. 
     The phrase “specifically (or selectively) binds (or detects)” a protein or peptide, when referring to an antibody, refers to a binding reaction that is determinative of the presence of the protein in a heterogeneous population of proteins and other biologics. Thus, under designated immunoassay conditions, the specified antibodies bind to a particular protein at least two times the background and do not substantially bind in a significant amount to other proteins present in the sample. Specific binding to an antibody under such conditions may require an antibody that is selected for its specificity for a particular protein. A variety of immunoassay formats may be used to select antibodies specifically immunoreactive with a particular protein. For example, solid-phase ELISA immunoassays are routinely used to select antibodies specifically immunoreactive with a protein (see, e.g., Harlow &amp; Lane, Antibodies, A Laboratory Manual (1988), for a description of immunoassay formats and conditions that can be used to determine specific immunoreactivity). Typically a specific or selective reaction will be at least twice background signal or noise and more typically more than 10 to 100 times background. “Immunoassay” is an assay that uses an antibody to specifically bind an antigen (e.g., a marker). The immunoassay is characterized by the use of specific binding properties of a particular antibody to isolate, target, and/or quantify the antigen. 
     Furthermore, the disclosure relates to a method as described above wherein the antibodies are part of an Enzyme-Linked Immunosorbent Assay. 
     The disclosure will be further illustrated by the following, non-limiting Examples. 
     Examples 
     List of Abbreviations 
     
         
         BHI Brain Heart Infusion 
         BW Body weight 
         CD Crypt depth 
         CD 3  Cluster of differentiation 3 
         CFU Colony forming units 
         DAB Di-amino-benzidine 
         DDA Data Dependent Acquisition 
         DFI Daily feed intake 
         DTT Dithiothreitol 
         DWG Daily weight gain 
         FCR Feed conversion ratio 
         HPLC-MS High performance liquid chromatography-mass spectrometry 
         HRP Horseradish peroxidase 
         LB Lysogeny Broth 
         MGAS Macroscopic Gut Appearance Score 
         MMTS Methyl methanethiosulfonate 
         MPDS 2 Mass prep digestion standard 2 
         MRS Man-Rogosa-Sharpe 
         MWCO Molecular weight cut-off 
         OTU Operational taxonomic unit 
         PBS Phosphate buffered saline 
         psi Pound per square inch 
         TEABC Triethylammonium bicarbonate 
         VL Villus length 
         VL/CD Villus-to-crypt ratio 
       
    
     Materials and Methods 
     Study Design 
     A total of 360 day-old broilers (Ross 308) were obtained from a local hatchery and housed in floor pens on wooden shavings. Throughout the study, feed and drinking water were provided ad libitum. The broilers were randomly assigned to two treatment groups, a control and challenge group (9 pens per treatment and 20 broilers per pen). All animals were fed a commercial feed till day 12 and the feed was switched to a wheat (57.5%) based diet supplemented with 5% rye (Table 1). From day 12 to 18, all animals from the challenge group received 10 mg florfenicol and 10 mg enrofloxacin per kg body weight via the drinking water daily, to induce substantial changes in the gut microbial community. After the antibiotic treatment, 1 ml of a bacterial cocktail consisting of  Escherichia coli  (G.78.71),  Enterococcus faecalis  (G.78.62),  Lactobacillus salivarius  (LMG22873),  Lactobacillus  crispatus (LMG49479),  Clostridium perfringens  (netB-) (D.39.61) and Ruminococcus gnavus (LMG27713) was given daily by oral gavage from day 19 till 21. Cultures of the bacteria were prepared as follows. Lysogeny Broth (LB, Oxoid,) was used for growing  E. coli. Enterococcus faecalis  and  C. perfringens  were grown in Brain Heart Infusion (BHI, Sigma) broth. Man-Rogosa-Sharpe (MRS, Oxoid) medium was used for the growth of  L. crispatus  and  L. salivarius . For the growth of  R. gnavus , anaerobic M2GSC medium (pH 6) as described by Miyazaki et al. (1997) was used but with 15% clarified rumen fluid instead of 30% and addition of 1 mg/ml cysteine HCl and 4 mg/ml NaHCO 3  after autoclaving.  E. coli  and  Enterococcus faecalis  was cultured in aerobic conditions at 37° C. In an aerobic (5% 02) incubator,  Lactobacillus  spp. were cultured.  C. perfringens  and  R. gnavus  were cultured an anaerobic chamber (gas mixture 84% N2, 8% 02 en 8% H 2 , GP[concept], Jacomex, France) at 37° C. The bacterial cells were collected by ultracentrifugation (10,000 rpm, 10 minutes, 20° C.) and each pellet was resuspended in 100 ml anaerobic phosphate buffered saline (PBS, 1 mg/ml cysteine HCl, pH 6). The resuspended pellets were mixed and diluted with anaerobic PBS to a total volume of 1.5:1 to reach a final concentration of about 109 colony-forming units (CFU)/ml for each bacterial strain (Table 2). On day 20, the animals were administered a coccidial challenge consisting of different  Eimeria  sp., namely 60,000 oocysts of  E. acervulina  and 30,000 oocysts  E. maxima.    
     At day 26, the birds were weighed and 3 birds per pen were euthanized. The duodenal loop was sampled for histological examination and content from ileum and colon was collected for protein extraction. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Composition and nutrient content of the wheat/rye based broiler diet. Starter 
               
               
                 diet was given till day 11. Grower was given from day 12 to day 34. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Starter 
                 Grower 
                 Calculated nutrient 
                 Starter 
                 Grower 
               
               
                 Feedstuff 
                 % 
                 % 
                 composition (%) 
                 % 
                 % 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Wheat 
                 55.13 
                 57.87 
                 Dry matter 
                 88.45 
                 88.38 
               
               
                 Rye 
                 0.00 
                 5.00 
                 Ash 
                 5.11 
                 4.79 
               
               
                 Soy meal, crude fiber 
                 22.86 
                 22.86 
                 Crude protein 
                 20.85 
                 18.98 
               
               
                 content &lt; 50 
               
               
                 Full fat soybeans 
                 7.50 
                 2.50 
                 Crude fat 
                 10.83 
                 9.90 
               
               
                 Animal fat 
                 7.20 
                 7.20 
                 Crude fiber 
                 2.93 
                 2.49 
               
               
                 Soybean oil 
                 1.00 
                 1.00 
                 Carbohydrates 
                 48.46 
                 51.95 
               
               
                 Premix 
                 0.50 
                 0.50 
                 Starch 
                 34.62 
                 38.46 
               
               
                 Lime fine 
                 1.11 
                 1.11 
                 Sugars 
                 4.77 
                 4.53 
               
               
                 Monocalcium 
                 0.83 
                 0.83 
                 NDF 
                 10.52 
                 9.93 
               
               
                 phosphate 
               
               
                 Salt 
                 0.18 
                 0.18 
                 ADF 
                 4.18 
                 3.52 
               
               
                 NaHCO 3   
                 0.25 
                 0.25 
                 Calcium 
                 0.69 
                 0.66 
               
               
                 L-lysine HCl 
                 0.30 
                 0.30 
                 Phosphorus, total 
                 0.57 
                 0.54 
               
               
                 DL-methionine 
                 0.30 
                 0.30 
                 Calcium/dP poultry 
                 0.22 
                 0.22 
               
               
                 L-threonine 
                 0.10 
                 0.10 
                 Magnesium 
                 0.16 
                 0.14 
               
               
                 Rapeseed meal &lt; 380 
                 2.74 
                 0.00 
                 Potassium 
                 0.88 
                 0.79 
               
               
                   
                   
                   
                 Sodium 
                 0.15 
                 0.15 
               
               
                   
                   
                   
                 Chloride 
                 0.20 
                 0.20 
               
               
                   
                   
                   
                 Base-excess (mEq/kg) 
                 23.39 
                 20.97 
               
               
                   
                   
                   
                 Linolic acid 
                 2.38 
                 1.92 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Broilers were orally inoculated with 1 ml of a bacterial cocktail 
               
               
                 on day 19, 20 and 21 with 10 6 -10 10  CFU of  Escherichia coli , 
               
               
                   Enterococcus faealis ,  Lactobacillus salivarius ,  Lactobacillus crispatus , 
               
               
                   Clostridium perfringens  (netB−) and  Ruminococcus gnavus   
               
            
           
           
               
               
               
               
            
               
                   
                 Day 19 
                 Day 20 
                 Day 21 
               
               
                 Bacterial strain 
                 (CFU/ml) 
                 (CFU/ml) 
                 CFU/ml) 
               
               
                   
               
               
                 
                   E. coli 
                 
                 2.11 × 10 9   
                 1.22 × 10 9   
                 2.28 × 10 9   
               
               
                 
                   Enterococcus faecalis 
                 
                 3.44 × 10 9   
                     2.28 × 10 10   
                 3.56 × 10 9   
               
               
                 
                   Lactobacillus salivarius 
                 
                 4.78 × 10 7   
                 1.16 × 10 7   
                 2.39 × 10 7   
               
               
                 
                   Lactobacillus crispatus 
                 
                 1.89 × 10 9   
                 7.78 × 10 7   
                 7.22 × 10 6   
               
               
                 
                   Clostridium perfringens 
                 
                   1 × 10 7   
                 1.06 × 10 7   
                 2.78 × 10 8   
               
               
                 
                   Ruminococcus gnavus 
                 
                 2.89 × 10 8   
                 2.78 × 10 8   
                 3.17 × 10 8   
               
               
                   
               
            
           
         
       
     
     Macroscopic Scoring System 
     The macroscopic appearance of the gut was evaluated using a previously described scoring system (Teirlynck et al., 2011), in which, in total, 10 parameters were assessed and assigned 0 (absent) or 1 (present), which resulted in a total score between 0 and 10. A total score of 0 represents a normal appearance of the intestinal tract while 10 points to severe deviations from the normal appearance. The parameters are (1) “ballooning” of the gut; (2) inflammation, cranial to the Meckel&#39;s diverticulum; (3) macroscopically visible and tangible fragile small intestine cranial to the Meckel&#39;s diverticulum; (4) loss of tonus in longitudinal cutting of the intestine cranial to the Meckel&#39;s diverticulum within the 3 seconds after incision; (5) abnormal occurrence of the intestinal content (excess mucus, orange content, gas) cranial to the Meckel&#39;s diverticulum; (6, 7, 8, 9) are identical to (2, 3, 4, 5) but caudal to the Meckel&#39;s diverticulum and (10) presence of undigested particles in the colon. A coccidiosis scoring was performed as described in Johnson &amp; Reid (1970) in which the animals were given a score for typical lesions associated with  Eimeria acervulina, E. maxima  and  E. tenella . For each, a score was given between 0 (absent) and 4 (severe). A total coccidiosis score was calculated as the sum of the scores given for lesions caused by each individual  Eimeria  species. 
     Morphological Parameters 
     The duodenal loop was fixated in 4% formaldehyde for 24 hours, dehydrated in xylene and embedded in paraffin. Sections of 4 μm were cut using a microtome (Microme HM360, Thermo Scientific) and were processed as described by De Maesschalck et al. (2015). Morphological parameters were determined using standard light microscopy. Villus length and crypt depth in the duodenum were measured by random measurement of twelve villi per intestinal segment using Leica DM LB2 Digital and a computer based image analysis program, LAS V4.1 (Leica Application Suite V4, Germany). Also the villus-to-crypt ratio was calculated. 
     Immunohistochemical Examination 
     Antigen retrieval was performed on 4 μm sections with a pressure cooker in citrate buffer (10 mM, pH 6). Slides were rinsed with washing buffer (Dako kit, K4011) and blocked with peroxidase reagent (Dako, S2023) for 5 minutes. Slides were rinsed with aqua destillata and Dako washing buffer before incubation with anti-CD 3  primary antibodies (Dako CD 3 , A0452) for 30 minutes at room temperature diluted 1:100 in antibody diluent (Dako, S3022). After rinsing again with washing buffer, slides were incubated with labelled polymer-HRP anti-rabbit (Envision +  System-HRP, K4011) for 30 minutes at room temperature. Before adding di-amino-benzidine (DAB + ) substrate and DAB +  chromogen (Dako kit, K4011) for 5 minutes, slides were rinsed 2 times with washing buffer. To stop the staining, the slides were rinsed with Aquadest, dehydrated using the Shandon Varistain-Gemini Automated Slide Stainer and counterstained with hematoxylin for 10 seconds. The slides were analyzed with Leica DM LB2 Digital and a computer based image analysis program LAS V4.1 (Leica Application Suite V4, Germany) to measure CD 3  positive area on a total area of 3 mm 2 , which represents T-lymphocyte infiltration in approximately 10 villi per section. 
     Discovery Proteomics 
     Sample Preparation 
     Individual colon and ileal content samples were collected and stored at −20° C. before use. 500 mg was solubilized in 10 ml 2 M urea, 50 mM ammonium bicarbonate and homogenized by vortexing. After centrifugation (20,000×g, 15 minutes, 4° C.), the supernatant was filtered through a 0.22 μm filter unit (Merck, Germany) directly in a Vivaspin 20 with a 5 kDa MWCO filter (Sartorius, Germany) and centrifuged for 1 hour at 4000×g. The filter was washed 3 times with 1 ml 2 M urea, 50 mM ammonium bicarbonate followed by centrifugation (4000×g, 10 minutes, 4° C.). The samples were washed 3 times with 1 ml 500 mM triethylammonium bicarbonate (TEABC, Sigma) to remove the urea. Subsequently, the samples were concentrated to a volume of ±500 μl. To determine the protein concentration, a Bradford assay was performed where OD was measured at 595 nm. Approximately 50 μg of proteins were reduced with 1 mM dithiothreitol (DTT) and incubated at 60° C. for 30 minutes, followed by alkylation for 10 minutes at room temperature with 10 mM methyl methanethiosulfonate (MMTS). Hereafter, calcium chloride and acetonitrile were added to a final concentration of 1 mM and 5% (v/v) respectively. Finally trypsin was added in a 1:20 (trypsin:protein) ratio for overnight digestion at 37° C. The samples were vacuum dried and analyzed with high performance liquid chromatography-mass spectrometry (HPLC-MS). 
     HPLC-MS 
     Peptides were dissolved in 0.1% formic acid in HPLC-grade water (buffer A) to a final concentration of 1 μg/μL. 100 fmol of mass prep digestion standard 2 (MPDS 2) was spiked into each sample. Data Dependent Acquisition MS analysis was performed on a TripleTOF 5600 (Sciex) fitted with a DuoSpray ion source in positive ion mode, coupled to an Eksigent NanoLC 400 HPLC system (Sciex). Peptides were separated on a microLC YMC Triart C18 column (id 300 μm, length 15 cm, particle size 3 μm) at a flow rate of 5 μL/minute by means of trap-elute injection (YMC Triart C18 guard column, id 500 μm, length 5 mm, particle size 3 μm). Elution was performed using a gradient of 4-40% buffer B (0.1% formic acid, 5% DMSO in 80% ACN) over 90 minutes. Ion source parameters were set to 5.5 kV for the ion spray voltage, 30 psi for the curtain gas, 13 psi for the nebulizer gas and 80° C. as temperature. 
     For DDA, a 2.25-second instrument cycle was repeated in high sensitivity mode throughout the whole gradient, consisting of a full scan MS spectrum (300-1250 m/z) with an accumulation time of 0.2 seconds, followed by 20 MS/MS experiments (50-1800 m/z) with 0.2 seconds accumulation time each, on MS precursors with charge state 2 to 5+ exceeding a 500 cps threshold. Rolling collision energy was used as suggested by the manufacturer and former target ions were excluded for 10 seconds. 
     Database Searching 
     The *.wiff files generated during LC-MS/MS analysis were imported into the Progenesis QI for Proteomics software (Non-linear Dynamics). The different samples were aligned based on retention time and m/z of reoccurring features to enable relative quantification. After subsequent peak picking, a merged *.mgf file was exported from the software and searched for identifications with MASCOT Daemon (Matrix Science, version 2.5.1) against a chicken database (reviewed protein database downloaded from Swissprot, January 2016) supplemented with the cRAP database (laboratory proteins and dust/contact proteins thegpm.org/crap/) and the internal standard. Maximum peptide mass tolerance and fragment mass tolerance were set to 10 ppm and 0.1 Da respectively. Additionally, methylthio on cysteine was set as a fixed modification and deamidation of asparagine and/or glutamine and oxidation of methionine were set as variable modifications. Enzyme specificity was set to trypsin with a maximum of one missed cleavage. The identifications were exported from MASCOT Daemon with a 5% false discovery rate (*.xml format) and imported into Progenesis QI for Proteomics. 
     Statistical Analysis 
     Statistical analysis was performed with Graphpad Prism (v.5). To evaluate whether the data is normally distributed, a Kolmogorov-Smirnov test was performed. In case of a normal distribution, comparison of the data was performed with an independent samples t-test. Otherwise, the non-parametric Mann-Whitney test was performed. A p-value of &lt;0.05 was considered statistically significant. The statistical coherence between different parameters was evaluated via correlation analysis. 
     Results 
     Performance Parameters 
     Body weight (BW), daily weight gain (DWG), daily feed intake (DFI) and feed conversion ratio (FCR) were measured during different time periods. Significant differences between treatment and control groups were seen at day 26, 35 and 41, but not at the age of 12 days (Table 3). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Mean ± standard deviation of body weight (BW), daily weight 
               
               
                 gain (DWG), daily feed intake (DFI) and feed conversion ratio (FCR) 
               
               
                 measured during different time periods for the control and challenge 
               
               
                 group. Significant differences (p &lt; 0.05) are shown in bold. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Control 
                 Challenge 
                   
               
               
                 Time period 
                 parameters 
                 Mean ± SD 
                 Mean ± SD 
                 p-value 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 D 1-D 12 
                 BW (g) 
                 290 ± 13 
                 295 ± 11 
                 0.485 
               
               
                   
                 DWG (g) 
                 19.6 ± 1     
                 20.2 ± 1     
                 0.342 
               
               
                   
                 DFI (g) 
                 24 ± 1 
                 25 ± 1 
                 0.614 
               
               
                   
                 FCR 
                  1.25 ± 0.06 
                  1.23 ± 0.05 
                 0.321 
               
               
                 D 12-D 26 
                 BW (g) 
                 1375 ± 58  
                 1195 ± 46  
                 
                   &lt;0.001 
                 
               
               
                   
                 DWG (g) 
                 78 ± 4 
                 64 ± 4 
                 
                   &lt;0.001 
                 
               
               
                   
                 DFI (g) 
                 116 ± 6  
                 108 ± 7  
                 
                   0.014 
                 
               
               
                   
                 FCR 
                  1.50 ± 0.07 
                  1.69 ± 0.18 
                 
                   0.004 
                 
               
               
                 D 26-D 35 
                 BW (g) 
                 2345 ± 174 
                 2153 ± 129 
                 
                   0.003 
                 
               
               
                   
                 DWG (g) 
                 106 ± 10 
                 105 ± 6  
                 0.857 
               
               
                   
                 DFI (g) 
                 185 ± 10 
                 203 ± 15 
                 
                   0.016 
                 
               
               
                   
                 FCR 
                  1.76 ± 0.14 
                  1.94 ± 0.20 
                 
                   0.040 
                 
               
               
                 D 35-D 41 
                 BW (g) 
                 3095 ± 164 
                 2850 ± 176 
                 
                   0.001 
                 
               
               
                   
                 DWG (g) 
                 121 ± 17 
                 114 ± 21 
                 0.276 
               
               
                   
                 DFI (g) 
                 161 ± 14 
                 166 ± 10 
                 0.427 
               
               
                   
                 FCR 
                  1.35 ± 0.14 
                  1.53 ± 0.45 
                 
                   0.041 
                 
               
               
                 D 12-D 35 
                 DWG (g) 
                 86 ± 5 
                 76 ± 4 
                 
                   &lt;0.001 
                 
               
               
                   
                 DFI (g) 
                 136 ± 6  
                 135 ± 8  
                 0.811 
               
               
                   
                 FCR 
                  1.59 ± 0.08 
                  1.79 ± 0.18 
                 
                   0.002 
                 
               
               
                 D 12-D 41 
                 DWG (g) 
                 91 ± 4 
                 82 ± 5 
                 
                   &lt;0.001 
                 
               
               
                   
                 DFI (g) 
                 139 ± 7  
                 140 ± 7  
                 0.864 
               
               
                   
                 FCR 
                  1.52 ± 0.04 
                  1.72 ± 0.13 
                 
                   &lt;0.001 
                 
               
               
                   
               
            
           
         
       
     
     Macroscopic Scoring 
     The appearance of the gut and a coccidiosis score were given to 27 birds per treatment. A lower body weight was observed at day 26 (p=0.0001) for broilers that received challenge treatment. The score for the macroscopic appearance of the gut and the total coccidiosis score were higher in the challenged group at day 26 (p&lt;0.001) ( FIGS.  1 A- 1 C , Table 4). 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Mean ± standard deviation of body weight (BW), macroscopic 
               
               
                 gut appearance score (MGAS) and coccidiosis score (CS) for the 
               
               
                 control (n = 27) and challenge group (n = 27) at day 26. 
               
               
                 Significant differences (p &lt; 0.05) are shown in bold. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Control 
                 Challenge 
                   
               
               
                 Timepoint 
                 parameters 
                 Mean ± SD 
                 Mean ± SD 
                 p-value 
               
               
                   
               
               
                 D 26 
                 BW (g) 
                  1375 ± 157.4 
                  1187 ± 170.1 
                 
                   p = 0.0001 
                 
               
               
                   
                 MGAS 
                 0.9 ± 0.7 
                 3.1 ± 1.1 
                 
                   p &lt; 0.001 
                 
               
               
                   
                 CS 
                 0.8 ± 0.7 
                 3.5 ± 1.7 
                 
                   p &lt; 0.001 
                 
               
               
                   
               
            
           
         
       
     
     Intestinal Morphology and Immunohistochemistry 
     A significant shorter villus length, an increased crypt depth, a lower villus-to-crypt ratio and a higher inflammation level in duodenal sections on day 26 (p&lt;0.0001) were detected in the gut of animals from the treatment group as compared to the control group (Table 5). 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Mean ± standard deviation of villus length (VL), crypt depth (CD), 
               
               
                 villus-to-crypt ratio (VL/CD) and T-lymphocyte infiltration (CD 3  area 
               
               
                 %) on day 26 for control (n = 27) and challenge group (n = 
               
               
                 27). For all evaluated parameters, statistical significance was p &lt; 0.0001. 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Control 
                 Challenge 
               
               
                 Timepoint 
                 parameters 
                 Mean ± SD 
                 Mean ± SD 
               
               
                   
               
               
                 D 26 
                 VL (μm) 
                 2035.7 ± 134.6 
                 1369.9 ± 158.7  
               
               
                   
                 CD (μm) 
                  190.1 ± 15.43 
                 365.7 ± 31.41 
               
               
                   
                 VL/CD 
                 11.03 ± 1.03 
                 3.85 ± 0.63 
               
               
                   
                 CD 3  area % 
                  7.88 ± 1.35 
                 9.54 ± 2.71 
               
               
                   
               
            
           
         
       
     
     Correlations 
     Pearson r has a value between −1 (total negative correlation) and +1 (total positive correlation). In case of a positive correlation, one parameter increases as the other parameter increases and vice versa. When one parameter decreases and the other one increases, there is a negative correlation. On day 26, all macroscopic (macroscopic gut appearance score, coccidiosis score and body weight) and histological parameters (villus length, crypt depth, villus-to-crypt ratio and T-lymphocyte infiltration) correlate with one another (Table 6). 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Pearson correlation coefficient between macroscopic gut appearance 
               
               
                 score (MGAS), coccidiosis score (CS), body weight (BW), villus 
               
               
                 length (VL), crypt depth (CD), villus-to-crypt ratio (VL/CD) and 
               
               
                 T-lymphocyte infiltration (CD3 area %). Correlation coefficients 
               
               
                 with a statistical significance of p &lt; 0.05 are shown. 
               
               
                 Day 26 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 CD 3   
               
               
                   
                   
                   
                   
                   
                   
                   
                 area 
               
               
                   
                 MGAS 
                 CS 
                 BW 
                 VL 
                 CD 
                 VL/CD 
                 % 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 MGAS 
                 — 
                   
                   
                   
                   
                   
                   
               
               
                 CS 
                 0.0905 
                 — 
               
               
                 BW 
                 −0.6836 
                 −0.5974 
                 — 
               
               
                 VL 
                 −0.8400 
                 −0.8572 
                 0.7400 
                 — 
               
               
                 CD 
                 0.8220 
                 0.8045 
                 −0.7546 
                 −0.9073 
                 — 
               
               
                 VL/CD 
                 −0.8507 
                 −0.8599 
                 0.7303 
                 0.9570 
                 −0.9773 
                 — 
               
               
                 CD 3   
                 0.8559 
                 0.8177 
                 −0.770 
                 −0.9028 
                 0.8959 
                 −0.8979 
                 — 
               
               
                 area % 
               
               
                   
               
            
           
         
       
     
     Discovery Proteomics 1. 
     Using MASCOT Daemon (Matrix Science, version 2.5.1) against a chicken database (reviewed protein database downloaded from Swissprot, January 2016) supplemented with the cRAP database (laboratory proteins and dust/contact proteins thegpm.org/crap/), 157 proteins were identified for colon. In theory, a good gut health biomarker should relate with one or more histological parameters since measurement of villus length and inflammation level are used as standard measurements in the evaluation of intestinal health. Also correlation with the macroscopic gut appearance score was evaluated. It is noted that proteins of which the colonic concentration has a negative correlation with the villus length, inverse correlation was seen with crypt depth, CD 3  area % and macroscopic gut appearance score. Only correlations with a statistical significance of p&lt;0.1 are shown (Table 7). 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Pearson correlation coefficient between the abundance of 
               
               
                 the protein in colon content and villus length (VL), crypt 
               
               
                 depth (CD), villus-to-crypt ratio (VL/CD) and T-lymphocyte 
               
               
                 infiltration (CD 3  area %) and macroscopic gut appearance 
               
               
                 score (MGAS) on day 26. Correlation coefficients with a 
               
               
                 statistical significance of p &lt; 0.1 are shown. 
               
               
                 Day 26 
               
            
           
           
               
               
               
               
               
            
               
                 Accession 
                   
                   
                   
                   
               
               
                 number 
                   
                 VL 
                 CD 3  area % 
                 MGAS 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 P08940 
                 Myeloid protein 1 
                 −0.7283 
                 0.5466 
                 0.5668 
               
               
                 P11722 
                 Fibronectin 
                 −0.8114 
                 0.6515 
                 0.6519 
               
               
                 P17153 
                 Annexin A5 
                 −0.5746 
               
               
                 P16039 
                 Nucleophosmin 
                 −0.5263 
                 0.7196 
               
               
                 P07630 
                 Carbonic anhydrase 2 
                 −0.5899 
                   
                 0.5726 
               
               
                 O57579 
                 Aminopeptidase Ey 
                 0.5462 
                   
                 −0.7177 
               
               
                 P27731 
                 Transthyretin 
                 −0.5778 
                 0.6065 
               
               
                 P10184 
                 Ovoinhibitor 
                 −0.4852 
               
               
                 P08250 
                 Apolipoprotein A-1 
                 −0.5066 
               
               
                   
               
            
           
         
       
     
     Discovery Proteomics 2 
     Using MASCOT Daemon (Matrix Science, version 2.5.1) against a chicken database (reviewed protein database downloaded from Swissprot, January 2016) supplemented with the cRAP database (laboratory proteins and dust/contact proteins thegpm.org/crap/), 157 and 181 proteins were identified for colon and ileum respectively whereby significant differential proteins between control and challenged birds were selected (p&lt;0.05). In broilers from the challenge group, the following proteins showed a significantly higher abundance compared to control animals in colonic content (p&lt;0.05): alpha-actinin-4 (ACTN4), annexin A5 (ANXA5), apolipoprotein A-1 (APOA1), fibronectin (FINC), hemoglobin subunit beta (HBB), myeloid protein 1 (MIMI), nucleophosmin (NPM), ovoinhibitor (IOV7) and transthyretin (TTR). Both in colonic and ileal content, superoxide dismutase [Cu—Zn] (SOD) showed a decreased abundance compared to control animals (p&lt;0.05). Angiotensin-converting enzyme (ACE), mitochondrial aspartate aminotransferase (AATM), cathepsin D (CATD), Ig lambda chain C region (LAC), Ig lambda chain V-1 region (LV1), TTR and WD repeat-containing protein 1 (WDR1) showed a lower abundance in challenged birds (p&lt;0.05) in ileal samples. Following proteins were more abundant (p&lt;0.05): APOA1, histone H2A-IV (H2A4) and retinol-binding protein 4 (RET4) (Table 8 and Table 9). 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Significantly different proteins between control 
               
               
                 and challenge group in colonic content. 
               
            
           
           
               
               
               
               
               
            
               
                 Accession 
                   
                   
                   
                 Highest 
               
               
                 number 
                 Protein name 
                 Abbreviation 
                 P-value 
                 mean 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Q90734 
                 Alpha-actinin 4 
                 ACTN4 
                 0.0385 
                 Challenge 
               
               
                 P17153 
                 Annexin A5 
                 ANXA5 
                 0.0266 
                 Challenge 
               
               
                 P08250 
                 Apolipoprotein A-1 
                 APOA1 
                 0.0277 
                 Challenge 
               
               
                 P11722 
                 Fibronectin 
                 FINC 
                 0.0106 
                 Challenge 
               
               
                 P02112 
                 Hemoglobin subunit 
                 HBB 
                 0.0158 
                 Challenge 
               
               
                   
                 beta 
               
               
                 P08940 
                 Myeloid protein 1 
                 MIM1 
                 0.0008 
                 Challenge 
               
               
                 P16039 
                 Nucleophosmin 
                 NPM 
                 0.0071 
                 Challenge 
               
               
                 P10184 
                 Ovoinhibitor 
                 IOV7 
                 0.0254 
                 Challenge 
               
               
                 P80566 
                 Superoxide dismutase 
                 SOD 
                 0.0287 
                 Control 
               
               
                   
                 [Cu—Zn] 
               
               
                 P27731 
                 Transthyretin 
                 TTR 
                 0.0317 
                 Challenge 
               
               
                   
               
            
           
         
       
     
     Proteomics using high performance liquid chromatography-mass spectrometry (HPLC-MS) was performed on colonic content of animals from the control (n=9) and challenged (n=9) group at day 26. This resulted in significant differential proteins (p&lt;0.05) with a higher normalized abundance of 9 proteins and a decrease of superoxide dismutase [Cu—Zn] in challenged birds. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Significantly different proteins between control 
               
               
                 and challenge group in ileal content. 
               
            
           
           
               
               
               
               
               
            
               
                 Accession 
                   
                   
                   
                 Highest 
               
               
                 number 
                 Protein name 
                 Abbreviation 
                 P-value 
                 mean 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 O57579 
                 Aminopeptidase Ey 
                 AMPN 
                 0.0012 
                 Control 
               
               
                 Q10751 
                 Angiotensin-converting 
                 ACE 
                 0.0006 
                 Control 
               
               
                   
                 enzyme 
               
               
                 P08250 
                 Apolipoprotein A-1 
                 APOA1 
                 0.0364 
                 Challenge 
               
               
                 P00508 
                 Aspartate 
                 AATM 
                 0.0067 
                 Control 
               
               
                   
                 aminotransferase, 
               
               
                   
                 mitochondrial 
               
               
                 Q05744 
                 Cathepsin D 
                 CATD 
                 0.0203 
                 Control 
               
               
                 P02263 
                 Histone H2A-IV 
                 H2A4 
                 0.0079 
                 Challenge 
               
               
                 P20763 
                 Ig lambda chain C 
                 LAC 
                 0.0155 
                 Control 
               
               
                   
                 region 
               
               
                 P04210 
                 Ig lambda chain V-1 
                 LV1 
                 0.0370 
                 Control 
               
               
                   
                 region 
               
               
                 P41263 
                 Retinol-binding 
                 RET4 
                 0.0399 
                 Challenge 
               
               
                   
                 protein 4 
               
               
                 P80566 
                 Superoxide dismutase 
                 SOD 
                 0.0004 
                 Control 
               
               
                   
                 [Cu—Zn] 
               
               
                 P27731 
                 Transthyretin 
                 TTR 
                 0.0091 
                 Control 
               
               
                 O93277 
                 WD repeat-containing 
                 WDR1 
                 0.0027 
                 Control 
               
               
                   
                 protein 1 
               
               
                   
               
            
           
         
       
     
     Proteomics using high performance liquid chromatography-mass spectrometry (HPLC-MS) was performed on ileal content of animals from the control (n=9) and challenged (n=9) group at day 26. This resulted in 12 significant differential proteins (p&lt;0.05) with a higher normalized abundance of apolipoprotein A-1 (APOA1), histone H2A-IV (H2A4) and retinol-binding protein 4 (RET4) and decrease in normalized abundance for the other 9 proteins in challenged birds. 
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