Intestinal microflora and expression of immunity-related genes in hens as influenced by prebiotic and probiotic feed additives

It is known that probiotic and prebiotic feed additive improve the function of the intestines and lead to normal the processes of digestion of food for animals. Colonization of the gastrointestinal tract with beneficial microflora helps to reduce the negative impact of pathogenic or conditionally pathogenic microorganisms, maintain optimal acidity of the gut, prevent dysbiosis, and stimulate local and general immune factors. However, the biological mechanisms for the implementation of such properties of these drugs are still not fully understood. We evaluated the effect of two Russian products, the multifunctional feed additive Profort® (Biotrof LLC, Russia), combining the qualities of an enzyme and probiotic, and the prebiotic feed additive Vetelact (SVC, Agrovetzashchita, Russia) on the quantitative and qualitative composition of the intestinal microbiota in egg layers to compare the effect of these feed additives on the intestinal microbiota with the expression of the b-defensin 9 (AvBD9), interleukin 8 (IL8), gallinacin-10 (Gal-10) and proenkephalin (PENK) genes that are associated with immune systems. Lohmann white LSL hens with an egg laying intensity of at least 95 % at the age of 25 weeks were used in the experiment (the conditions of vivarium, 2019). The hens were assigned to three groups (20 birds each). Feeding the birds was carried out with mixed feed, the feed specification were calculated according manual from Lohmann Tierzucht. Birds of the control group received only mixed feed. Birds of the experimental groups were also fed with biological additives for 28 days. The egg production was recorded daily, the egg laying intensity, egg weight and body weight were recorded weekly. After the termination of the experiment, the composition of the microbiota of the blind processes of the intestine was determined using NGS sequencing and the expression levels of the b-defensin 9 ( AvBD9 ), interleukin 8 ( IL8 ), gallinacin-10 ( Gal-10 ), and proenkephalin ( PENK ) genes were assessed. It is known that b-defensin 9 and gallinacin-10 belong to the family of endogenous peptides, which are an important element of the innate immunity system and a link between innate (non-specific) and acquired (adaptive, specific) immunity, proenkephalin is one of six opioid peptides that regulate signaling between cells and affect many biological processes in vertebrates, including development, growth and reproduction, and interleukin 8 is one of the main pro-inflammatory chemokines formed by macrophages, epithelial and endothelial cells which also plays an important role in the innate immune system. It was established that the hens receiving probiotic had the highest egg productivity (3.33 % higher than the control, p 0.05) decrease in egg production with the body weight 0.9 % (p > 0.05) higher compared to the control. Feeding the prebiotic contributed to an increase in the total number of microorganisms in the intestinal contents to 7.625±0.74 lg CFU/g (the microbial number in the control was 7.598±1.01 lg CFU/g), while the feeding with probiotic reduced the number of microorganisms to 7.565±0.56 lg CFU/g (p > 0.05). Both feed additives contributed to an increase in the number of bifidobacteria and cellulolytic bacteria in the intestine and reduced the total amount of pathogenic and undesirable microflora by 25-50 % vs. control. A decrease in the proportion of pathogenic and undesirable microorganisms in the composition of microbiota naturally reduced the body’s need for non-specific defense factors and pro-inflammatory cytokines. In the birds receiving feed additives, the expression of the b-defensin 9 gene was 3.3-5.0 times lower, and the interleukin 8 ( IL8 ) gene expression level was reduced by 8-36 % compared to the control. Along with a decrease in the expression of b-defensin 9 and interleukin-8 genes, a 1.48-1.55-fold increase in the expression of the gallinacin-10 gene and 1.11-1.91-fold increase in proenkephalin were established, which is probably associated with strengthening the protective functions of the body. The selective effect of probiotic and prebiotic on the reproduction of various types of bacteria in the intestine, confirmed by the negative expression of genes associated with immunity, justifies the promise of using the studied products to increase the resistance of poultry and normalize functions of the immune system without compromising of poultry performance.