Effect Of Lactobacillus On The Cecum Microbiome And Mucosal Barrier Of Broilers Under Heat Stress

Heat stress affects the composition and structure of intestinal microbiome,triggers intestinal inflammation,destroys intestinal mucosal barrier,affects the health and production performance of poultry,and leads to huge economic losses.Lactobacillus can inhibit the adhesion of pathogenic bacteria to epithelial cells,alleviate the damage of pathogenic bacteria induced inflammatory cytokines to tight junction,promote the expression and reasonable distribution of tight junction proteins in epithelial cells,and maintain the barrier function of epithelial cells and the integrity of mucosa.However,the effect of different strains is very different.In this study,we compared the effects of different Lactobacillus on cecal microbiota and mucosal barrier of in heat stressed broilers,and screened Lactobacillus which can regulate the composition of intestinal microbiome,reduce mucosal inflammatory response and alleviate the adverse effects of high temperature on the intestinal health of broilers.It provides a theoretical basis for improving the health and production performance of broilers in summer through nutritional measures in the future.A total of 648 one-day-old AA male broilers were randomly divided into 6 groups:control temperature group(CT),high temperature group(HT)and four Lactobacillus groups.The CT and HT groups were fed the basic diet,and the four Lactobacillus groups were fed the basic diet with 10~9 cfu/kg of Lactobacillus rhamnosus(LR),Lactobacillus plantarum A(LPA),Lactobacillus casei(LC)and Lactobacillus plantarum B(LPB),respectively.Each treatment consisted of nine replicates,and each replicate had 12 birds(CT and HT group contained 14 and 10 birds,respectively).Six treatment groups were transferred to environment chambers,respectively.Adjust the temperature according to the AA broiler management manual for 1-28 days old,and the temperature of 6 environmental chambers should be consistent.At 28 days of age,the CT group was continued to maintain 21±1℃,the HT group and four Lactobacillus groups were gradually increased the temperature to 31±1℃,and continued to the end of 42-day-old trial.The study found:1)The species richness of cecal microbiota in broilers increased with the increase of age,and the diversity and composition of the microbiome changed significantly.High temperature had no significant effect on the diversity of broiler(P>0.05)at 4 days of heat stress(32 days old)and 14 days of heat stress(42 days old).Heat stress for 4 days significantly affected the relative abundance of Xanthomonadaceae and Ruminococcaceae(P<0.05),which was contrary to the change direction of the dominant bacteriaceae of broilers at 42 days old.There was no significant effect on the relative abundance of 8 dominant families of cecum in broilers under heat stress for 14 days(P>0.05).After 4days of heat stress,the addition of 4 strains of Lactobacillus showed a tendency to alleviate the effect of high temperature on cecum dominant bacteriaceae(P<0.1).The 4 strains of Lactobacillus on 14 days of heat stress had no significant effect on the composition of dominant cecal microbiota in broilers(P>0.05).2)The effect of high temperature on the cecal mucosal barrier of broilers supplementation with Lactobacillus was alleviated.The expression of IL-8 mRNA in cecal mucosal of broilers was significantly increased(P<0.05)at 4 days of heat stress(32 days old).The expression of TGF-βmRNA at 14 days of heat stress(42 days old)was significantly decreased(P<0.05)and the expression of IL-8and TNF-αmRNA were increased(P<0.05).The expression of Occludin and ZO-1 m RNA in cecal mucosal of broilers were significantly decreased(P<0.05),and the expression of MLCK mRNA was significantly increased(P<0.05)at different time of heat stress.The addition of LPA,LC and LPB could significantly alleviate the increase of heat stress-induced inflammatory cytokines(P<0.05)and significantly alleviate the effect of high temperature on the tight junction protein(P<0.05),while LR had no significant effect.3)High temperature for 4 days significantly affected the ability of broilers cecal fluid to resist Salmonella colonization,and Lactobacillus could alleviate the influence of heat stress.Feeding 1day-old chicks to the 32-day-old CT group of broiler cecal fluid significantly reduced the number of Salmonella in the chick cecal(P<0.05),but feeding the 32-day-old HT group of cecal fluid had no significant effect on the number of Salmonella in the chick cecum(P>0.05);The addition of LPA,LC and LPB significantly improved the resistance of broiler cecum fluid to Salmonella colonization under heat sress(P<0.05).The 42-day-old CT,HT and 4 strains of Lactobacillus group significantly reduced the colonization of Salmonella cecum in broilers(P<0.05).4)The LPA,LC and LPB affected the relative abundance of some dominant bacteriaceae in broilers before heat stress(21 days old),which was consistent with the change direction of the relative abundance of dominant bacteriaceae in broilers at 32 days old.The expression of pro-inflammatory cytokines in caecal mucosa of 21 days old broilers supplementation with 4 strains of Lactobacillus were significantly decreased(P<0.05),among which LPA,LC and LPB had significant effect.The LPA and LC significantly increased the expression of tight junction protein(P<0.05)and decreased the expression of MLCK(P<0.05).The LPB had the trend to improve the expression of tight junction protein.The above results showed that the effects of different strains of Lactobacillus were significantly different on cecal microbiota and mucosal barrier.Among them,Lactobacillus plantarum A and Lactobacillus casei can regulate the composition of cecal microbiota,reduce the expression of inflammatory cytokines,improve the expression of mucosal tight junction protein,alleviate the effect of heat stress on cecal microbiota and mucosal barrier,and improve the ability of heat stress broiler cecal fluid against Salmonella colonization;Lactobacillus plantarum B can effectively alleviate the adverse effects of heat stress.However,Lactobacillus rhamnosus had no significant effect on the mucosal barrier of broilers before and after heat stress.