Changes of haematological and biochemical indices with age in rabbits with ad libitum and limited feed intake

The aim of this study was to examine the effects of a one-week feed restriction of different intensities on haematological and biochemical blood indices at the end of the feed restriction and during the realimentation period in growing rabbits. Hyplus rabbits weaned at 35 days of age (n = 195) were divided into three groups: rabbits fed ad libitum (AL) and groups with reduced feed of 50 g (R50) or 65 g (R65) per rabbit per day from 42 to 49 days of age. At the end of the feed restriction and in the following period, haematological and biochemical blood indices were measured at weekly intervals. The live weight at 70 days of age was lower (P ≤ 0.001) in restricted rabbits (–14.5% and –15.5% for group R50 and R65, respectively, compared to AL). Feed restriction significantly (P ≤ 0.011) decreased the number of erythrocytes (–6.2% and –7.4% for group R50 and R65, respectively, compared to AL) and haemoglobin content (P ≤ 0.008). The mean corpuscular volume increased (P ≤ 0.033) in restricted rabbits. Interaction of the feeding regime and age (P ≤ 0.007) was observed in cholesterol with the highest concentration in R50 at 56 days (4.41 mmol/l) and the lowest in R65 at 70 days and in AL at 63 days of age (1.30 mmol/l). The concentration of non-esterified fatty acids (P ≤ 0.003) and triacylglycerides (P ≤ 0.048) were significantly lower in restricted rabbits. It could be concluded that feed restriction influenced mainly erythrocytes and haemoglobin. The changes in biochemical blood characteristics suggest the restriction did not affect protein metabolism, however, results indicate lipid depletion in restricted rabbits. Hyplus, feed restriction, blood, metabolic characteristic Limited feed intake is applied in growing rabbits as a prevention of digestive disorders around the post-weaning age (Di Meo et al. 2007). It has been reported to improve feed efficiency (Tůmová et al. 2003; Di Meo et al. 2007; Gidenne et al. 2009, 2012) and to reduce carcass fat deposition (Gondret et al. 2000; Tůmová et al. 2003, 2007). Blood characteristics in rabbits are used for clinical diagnosis of organic, infectious and several parasitic diseases, detecting stress conditions, and assessing the metabolic condition of animals (Archetti et al. 2008; Çetin et al. 2009). Haematological and biochemical blood indices are influenced by numerous factors including the breed (Martinec et al. 2012), sex (Çetin et al. 2009), age (Jeklova et al. 2009), diurnal and seasonal variation (Çetin et al. 2009), physiological condition (Wells et al. 1999), and nutrition (Addass et al. 2012). Haematological constituents reflect the physiological responsiveness of the animal to the internal and external conditions which include feeding (Etim et al. 2014). There is a lack data of the effect of the feeding regime on haematology in rabbits. For example, Tůmová et al. (2007) stated that most haematology indices in rabbits were not affected by feed restriction, only the lymphocyte counts were increased and neutrophil counts were reduced in the restricted group. In domestic fowl, haemoglobin was reduced when broilers were exposed to stress caused by feed restriction, whereas the number of erythrocytes increased significantly (Maxwell et al. 1990). ACTA VET. BRNO 2017, 86: 29–35; https://doi.org/10.2754/avb201786010029 Address for correspondence: Darina Chodová Department of Animal Husbandry Czech University of Life Sciences Prague Kamýcká 129, Prague 6, Suchdol, 165 21, Czech Republic Phone: +420 224 382 309 E-mail: chodova@af.czu. cz http://actavet.vfu. cz/ After the end of the feed restriction, when animals are fed ad libitum again, various degrees of compensatory growth can be exhibited in rabbits. These changes in growth during feed restriction and the following realimentation period can be manifested in the proteolytic enzyme function and metabolic processes in the organism represented in changes of biochemical blood indices. There is a lack of information regarding the effect of feed restriction on the biochemical characteristics in rabbits. Van Harten and Cardoso (2010) found that the glucose concentration was not affected by feed restriction in the New Zealand rabbit. Likewise, Sartory et al. (1995) reported that blood glucose concentrations in birds seemed markedly resistant to prolonged feed deprivation. In contrast, Rommers et al. (2004) observed a lower glucose concentration during the period of feed restriction in rabbit does. According to Kersten et al. (1999), fasting decreased adipose tissue lipogenesis and increased the rate of lipolysis. Similarly, van Harten and Cardoso (2010) detected a lower concentration of non-esterified fatty acids (NEFA) and triacylglycerides (TAG) in restricted rabbits. On the other hand, Rommers et al. (2004) observed a similar concentration of NEFA and plasma urea nitrogen in rabbits fed ad libitum and restricted rabbits during the time of feed restriction, however, in the following period, these authors detected higher NEFA as well as TAG concentrations in rabbits fed ad libitum. Data inconsistencies may be affected by the method of feed restriction, its commencement, and duration. The aim of the current study was to evaluate the effects of a one-week feed restriction with different intensities on haematological and biochemical indices at the end of the feed restriction and during the realimentation period. Materials and Methods The effects of a one-week intensive feed restriction in Hyplus rabbits (PS 19 × PS 59) were studied. The experiment was approved by the Ethics Committee of the Central Commission for Animal Welfare at the Ministry of Agriculture of the Czech Republic. Weaned rabbits with similar live weights at 35 days of age (n = 195) were divided into three experimental groups: rabbits fed ad libitum (AL); rabbits with a limited feed intake of 50 g per animal per day from 42 to 49 days of age (R50); and rabbits with a limited feed intake of 65 g per animal per day from 42 to 49 days of age (R65). The rabbits were housed in wire net cages with a stocking density of 3 rabbits per cage (floor density of 0.16 m2 per rabbit). Before and following the feed restriction, the rabbits were fed ad libitum. Water was available ad libitum for all groups throughout the whole experiment. Rabbits were fed using a commercial pelleted diet containing 17.1% crude protein, 20.7% crude fibre, and 2.8% ether extract. Environmental conditions were the following: temperature 15–17 °C, relative humidity 55–60% and lighting regime 12 L:12 D. The live weight was recorded at 35, 42, 49, and 70 days of age. Blood was taken from the jugular vein from eight rabbits per each treatment at the end of the feed restriction at 49 days of age and at weekly intervals. The samples (n = 96) for haematological examination were taken into tubes containing dipotassium salt of ethylenediamine tetraacetic acid (K2EDTA). Detection of haematological characteristics was carried out in samples stored at 4 °C within 24 h after blood collection. The erythrocyte count, leukocyte count, haemoglobin concentration and haematocrit were detected using an automatic haematological analyser Coulter Model ZF (Coulter Electronics Ltd., England). The leukocyte count was detected by staining using the Pappenheim method. The mean cell volume (MCV) was calculated from the erythrocyte count and haematocrit values. Samples for biochemical evaluation (n = 96) were collected into tubes without an anticoagulant agent. Blood serum was separated by centrifugation of samples at 1,000 g for 10 min and then stored at –70 °C until analysis. Biochemical indices including concentrations of total protein, urea, glucose, cholesterol, NEFA, and TAG were determined using the commercial set Randox (Randox Laboratories Ltd., Crumlin, UK) and using the spectrophotometer Libra S22 (Biochrom Ltd., UK). The values of blood biochemical indices were determined by counting from the absorbance. The results were processed by two-way analysis of variance ANOVA (with interaction between group and age) using the general linear model (GLM) procedure of statistical analysis system (SAS Institute Inc. 2003). A P value of ≤ 0.05 was considered significant for all measurements.