Age dynamics of pancreas secretory function and intestinal microbiota in meat broiler chicks and their parental lines

The distinctive feature of avian digestion is high activities of the digestive enzymes. The digestion of poorly hydrolysable feed ingredients is known to be partially performed by microbial communities of cecum and large intestine (B. Svihus et al., 2013). The aim of our study was the investigation of embryonic and postembryonic enzymatic and microbial digestive processes in the intestine of meat-type chicken of parental lines B5 (Cornish), B9 (Plymouth Rock) and final hybrids (B59 Smena 8 cross) of «Smena» Selective-Genetic Centre (Russia) on ontogenesis (7- and 14-day old embryos, and 1-, 7-, 14-, 21-, 28-, and 35-day old chicks; 20 incubated eggs and 20 chicks per age in total; the experiment was carried out in the vivarium of All-Russian Research and Technological Poultry Institute). Activity of pancreatic enzymes (amylase and lipase) was detected in homogenates of the whole embryos (day 7 of incubation) and the embryonic intestinal and pancreatic tissues (day 14 of incubation). In day-old chicks high levels of pancreatic enzymes in the pancreas were found with no significant differences between parental lines and final hybrids in early postnatal period. According to the exocrine function of the pancreas, postnatal ontogenesis can be divided into two periods. In 1-14 day-old chicks the pancreas and its digestive function intensively develop, and the next period (from day 15 to day 35) is necessary to reach physiological maturity of the organ which becomes capable of enzyme production and secretion adequate to the diet. The activity of blood pancreatic amylase and proteases tended to decrease with age, and lowered significantly on day 35. The lipase activity followed the inverse trend and sinuously increased to day 35 (P ≤ 0.05). The percentage of cellulolytic bacteria in intestinal microbiota reached its peak on day 14 without significant differences between the hybrids (50.79±1.84 %) and the parental lines (50.84±2.32 and 53.23±2.47 %). This percentage subsequently decreased by 60.0 % in the hybrids from day 14 (50.80±1.84 %) to day 35 (20.30±0.85 %), while in the parental lines there were sinuous variations throughout this period with 41.00±1.87 % and 44.80±2.27 % on day 35 in Plymouth Rock and Cornish, respectively. These data suggests a negative correlation between activity of pancreatic proteases and intestine cellulolytic bacteria. The highest r values were noted for Clostridium (-0.64, -0.83 and -0.64 for Cornish, Plymouth Rock and the hybrid chicks, respectively). The proportion of Lactobacillales that participate in feed fermentation positively correlated with the activity of amylase, lipase and protease in the hybrids ( r = 0.71, r = 0.56, and r = 0.83) and in the Plymouth Rock line (r = 0.60, r = 0.46, and r = 0.45). A positive correlation was mostly found between the activity of pancreatic enzymes and the development of opportunistic and pathogenic microflora, i.e. Enterobacteriaceae (for amylase, lipase and proteases r = 0.65, r = 0.59, r = 0.68 in the hybrids, and r = 0.34, r = 0.68, r = 0.64 in the Cornishes, respectively), Staphylococcus (for protease r = 0.46 in the Cornishes, for amylase and proteases r = 0.70 and r = 0.91 in the Plymouth Rock line), Campylobacterium (for proteases r = 0.86 in the hybrids) and Fusobacterium (for amylase and proteases r = 0.41 and r = 0.90 in hybrids, for lipase and protease r = 0.63 and r = 0.83 in the Cornishes, for amylase and proteases r = 0.99 and r = 0.92 in the Plymouth Rock line). Thus, the intensive development of individuals is due to the activity of digestive enzymes which is interrelated with the quantitative and qualitative composition of the intestinal microbiota. Regarding the analyzed indicators, embryogenesis and early post-embryonic periods should be considered crucial for chicken development.