Response to dietary supplementation of mixtures
of either selected synbiotic, organic acids or essential oils
as growth promoters for growing Japanese quails

The present study was aimed to compare the efficacy of natural dietary supplementations (either synbiotics, organic acids or essential oils) in promoting productive performance and health status of growing Japanese quails. In total, 840 unsexed quail chicks aged 14 days, were randomly distributed into four groups of 210 birds in seven replicates, 30 birds each. The first group was fed un-supplemented control diet, the other groups were supplemented with: i) a mixture of live Saccharomyces cerevisiae, Bacillus spp. and their cell wall extracts, in addition to β-glucan and mannan-oligosaccharides as synbiotics; ii) a mixture of formic and propionic acids as organic acids; or iii) a mixture of carvacrol, cinnamaldehyde and capsicum oleoresin as essential oils; at a level of 1 g, 0.5 g and 0.15 g per kg diet, respectively. It was indicated that birds fed diets supplemented with either examined mixture of essential oils or organic acids had significantly higher body weight and better feed conversion ratio than the control group (by 5.4 and 4.9%, and 10.3 and 8.8%, respectively). It was also revealed that all studied growth promoters significantly increased the abdominal fat percentage. Both groups treated with mixture of either essential oils or organic acids recorded significantly higher villi height and width with lower total bacterial count and Escherichia coli enumeration than the control one. In conclusion, both examined mixtures of either essential oils (with carvacrol, cinnamaldehyde and capsicum oleoresin) or organic acids (formic and propionic acids) could be used in quail diets as organic growth promoters as they enhance growth performance by improving blood parameters and gut health status. 1 Corresponding author: e-mail: assemsafwat2004@yahoo.com 2 Different growth promoters in quail diets host body. Synbiotics (such as mixture of prebiotics including mannan-oligosaccharides or β-glucan and probiotics containing different Lactobacillus spp., Bifidobacterium bifidum, Streptococcus salivarius spp. and Enterococcus faecium) beneficially alter the intestinal microbiota composition and improve structural histomorphology of the intestinal mucosa providing better intestinal health for the bird to obtain maximum nutrient absorption (Sohail et al., 2012), additionally, β-glucan and mannanoligosaccharides are well-known as antioxidant and immunocompetent agents (Rageb et al., 2018). Another type of compounds are the organic acids (e.g., formic and propionic acids) that modify the intestinal pH and reduce the numbers of pathogenic bacteria through cell-wall penetration, in addition to increase acid-tolerant beneficial species such as Lactobacilllus spp. and reduce competition for nutrients by the altered microbes (Goodarzi Boroojeni et al., 2014). Meanwhile, essential oils compounds (e.g., cinnamaldehyde, thyme oil, carvacrol or capsaicin) proposed several mechanisms that include antimicrobial activity against pathogens, antioxidant activity, enhancing the function and regeneration of erythrocytes, stimulating carbohydrates and lipids metabolism in addition to their anti-allergenic effects (Jamroz et al., 2003; Sengül et al., 2008; Abd El-Hack et al., 2020; Krauze et al., 2021). There are some important measurements, beside the productive performance, that evaluate the effects of dietary growth promoter substances on animal health such as studying blood profile (including haematological parameters, protein and lipid profiles as well as liver and kidney functions) which could be used as an indicator for the physiological status and the welfare condition of birds (Moniello et al., 2005), intestinal histopathology and microbial ecology of animals (Incharoen et al., 2010; Abd-Allah and Abdel-Raheem, 2012). There were published several researches with conflicting results regarding the role of natural growth promoters (including probiotics of Saccharomyces cerevisiae and Lactobacillus spp., prebiotics of β-glucan and mannan-oligosaccharides, formic acid, propionic acid, carvacrol, cinnamaldehyde and capsicum oleoresin) in stimulating poultry performance, as these effects depend on the form and/or source of such compounds, bacterial species to be resisted, animal species and the growth promoter site of action (Hassan et al., 2010; Fascina et al., 2012; Oleforuh-Okoleh et al., 2015); however, the complete information of such compounds on quail performance is still scarce. In this context, an integrated study is required to evaluate different compounds as antibiotic growth promoter alternatives for organic Japanese quail production. In this paper, it was hypothesized that dietary supplementation of either synbiotics, organic acids or essential oils could promote growth through enhancing gut health and physiological status of Japanese quails. Therefore, the objective of the present study was to evaluate the efficacy of three different mixtures of natural growth promoters: (1. live S. cerevisiae, Bacillus spp., β-glucan, and mannan-oligosaccharides as synbiotics; 2. formic and propionic acids as organic acids; 3. carvacrol, cinnamaldehyde and capsicum oleoresin as essential oils) in improving productive performance and health status of growing Japanese quails. Material and methods