Effect Of Probiotics On Intestinal Structure And Expression Of Innate Immune Related Genes In Heat-stressed Broilers

Heat stress is an important factor affecting the poultry production performance,reproductive performance and product quality in our country,and it is prone to outbreak of various diseases.High-temperature stress leads to impaired intestinal function in livestock and poultry,and the intestinal microbial balance is destroyed,resulting in a decrease in intestinal immunity.The effect and mechanism of heat stress on the intestinal immune function of livestock and poultry,especially the intestinal immune response,are rarely reported.Probiotics,as a class of microorganisms with favorable host activity,are now widely accepted and replaced by antibiotics in diets.Probiotics can improve intestinal function,facilitate intestinal absorption and digestion of nutrients,and promote the growth and development of livestock and poultry..Therefore,to carry out changes in the intestinal immune function of livestock and poultry under heat stress conditions and to understand its regulatory mechanisms,to enrich the theory of heat stress,effectively improve the damage caused by heat stress has important theoretical and practical significance.The purpose of this study was to investigate the effect of probiotics on growth performance,immune organ index,antioxidant index,intestinal microflora structure,and expression of innate immune-related genes in heat-stressed broiler chickens.Three hundred healthy AA broiler chickens aged 1 day were routinely fed to 21 days of age.Two hundred and forty broilers with similar healthy weights were randomly divided into four groups.Each group consisted of four replicates with 15 chickens per replicate.The probiotics fed were Lactobacillus rhamnosus,Lactobacillus fermentum,and Enterococcus faecium,which were added to the basal diet to achieve a viable cell count of 109 cfu/kg.the above.This test uses a 2×2 two-factor design.The four groups were treated as follows: appropriate temperature control group,feeding basal diet;appropriate temperature + probiotic group,feeding basal diet + probiotics;heat stress group,feeding basal diet;heat stress + probiotic group,feeding basal diet + probiotics.The temperature in the suitable temperature group is maintained at about 22-24°C,and the temperature in the heat stress group is maintained at a temperature of 28°C-35°C-28°C for a daily cycle.Samples were taken at 28,35,and 42 days of broiler chicks,respectively.Blood was collected from the wing veins and used to measure serum anti-oxidation parameters.The peritoneal cavity was sacrificed and the thymus,spleen,and bursa were isolated.The duodenum,jejunum,and the middle ileum were cut at 4 cm to determine the morphological structure of the intestine.The ileal contents and mucosa were collected under aseptic conditions to determine the diversity of microorganisms;jejunum tissue was collected for detection of the expression of related genes.The test results are as follows:1 Heat stress significantly reduced the intake of broilers in the three stages(21st to 28 th,28th to 35 th,and 35 th to 42 th days of age)(P<0.05).At 21-28 days of age,Heat stress significantly increased the feed-to-weight ratio,adding probiotics significantly increased daily gain,significantly reduced feed-to-weight ratio(P<0.05);at 35-42 days of age,heat stress was significantly higher than the suitable temperature control group.Reduce the average daily gain(P<0.05).Heat stress significantly reduced the index of immune organs in broiler chickens(P<0.05),and the effect of probiotics was not significant.2 Heat stress significantly reduced duodenal villus height in three stages of broiler intestine(P<0.05),and the ratio of villus height and crypt depth in duodenum of heat-stressed broilers was significantly decreased at 28-35 days of age.(P<0.05)Adding probiotics can significantly increase the villus height of the ileum at 21 st to 28 th day and 28 th to 35 th days of the broiler duodenum and 35-42 days of ileum(P<0.05).Heat stress significantly increased glutathione peroxidase(GSH-Px)activity and glutathione(GSH)content in broilers(P<0.05).3 Heat stress affected the microbial content of the ileum of broiler chickens,and significantly reduced intestinal tract mucosa of the 42-day-old broiler,such as thick-walled bacillus,significantly increased intestinal contents of broiler chickens at the age of 42 days(P<0.05).The addition of probiotics to the diet had a tendency to reduce the content of Streptococcus(P=0.053).The addition of probiotics to the diet had no significant effect on the diversity and richness of the flora.4 Heat stress significantly reduced the expression of TLR2 gene in the jejunum of 35-day-old broilers and increased the expression of TLR15 gene in the jejunum of 28-day-old broilers.The addition of probiotics to diets increased the expression of TLR2 and Cathelicidin-B1 genes.In conclusion,heat stress reduces the growth performance of broilers,and the addition of probiotics to the diet can improve the growth of broilers.Heat stress destroys the intestinal structure of broilers.Adding probiotics to the diet can improve intestinal structure.Heat stress destroys the antioxidant enzyme system in broiler chickens.Adding probiotics to the diet can improve the antioxidant capacity of broiler chickens.Heat stress destroys the structure of intestinal microbiota and changes the expression of natural immune-related genes.The addition of probiotics to feed can improve the expression of natural immune genes.