| High environmental temperatures lead to heat stress in pigs,which seriously reduces growth performance and organism health and restricts the development of pig industry.The intestine,as the first barrier of the body’s immune defence,has become a hot spot for heat stress research in pigs in recent years.Epigallocatechin gallate(EGCG)is a polyphenolic compound isolated from green tea,which has anti-inflammatory and immune enhancing effects.In this study,a heat stress model was constructed to study the effects of EGCG on the intestinal barrier function of Bama xiang pigs under heat stress and its mechanism,so as to provide a scientific basis for the future development of EGCG as a green feed additive that can alleviate heat stress and improve the intestinal health of pigs by regulating the intestinal barrier function.The main research contents and results are as follows:1.Effect of EGCG on the growth performance,physiological and biochemical indexes of Bama xiang pigs under heat stressTwenty-five 8-month-old male Bama xiang pigs with an average weight of 34 kg were randomly divided into five treatments,with five pigs in each group: The first group was the normothermic control group(TN group,22 ℃,feeding freely),The second group was the normothermic pair feed group(PF group,22 ℃,pair feed),and the other three groups were the 35 ℃ high temperature group,and the diets were supplemented with 0% EGCG(HS0group,free feed),0.025% EGCG(HS250 group,feeding freely)and 0.05%EGCG(HS500 group,feeding freely),respectively.The formal test lasted for28 d.The pigs were slaughtered and blood was collected at the end of the trial to determine growth performance,blood physiological and biochemical parameters.The results showed that:(1)Heat stress significantly increased the concentration of heat shock protein HSP70 in the serum of Bama xiang pigs,while EGCG significantly reduced the concentration of HSP70 in the serum of Bama xiang pigs under heat stress.(2)Heat stress significantly increased the rectal temperature and respiratory rate of Parmesan pigs,significantly reduced their final weight,average daily weight gain and average daily feed intake,and increased the feed-to-weight ratio,while EGCG could significantly reduce the rectal temperature and respiratory rate of Bama xiang pigs under heat stress and improve their growth performance.(3)Heat stress significantly increased the serum concentrations of GLB,ALT,UREA and inflammatory factors IL-6 and IL-8,while significantly decreasing the concentrations of GLU.EGCG significantly decreased the serum concentrations of GLB,ALT,UREA and inflammatory factors IL-6 and IL-8,while significantly increasing the concentrations of GLU in Bama xiang pigs under heat stress.(4)Heat stress significantly increased the total leukocyte,granulocyte,and granulocyte ratios,while significantly decreasing the total erythrocyte and hemoglobin concentrations in the blood.EGCG significantly decreased the total leukocyte,granulocyte,and granulocyte ratios,while significantly increasing the total erythrocyte and hemoglobin concentrations in the blood of Bama xiang pigs under heat stress.In conclusion,the successful establishment of the heat-stressed Bama xiang pigs model had laid the foundation for the subsequent research using this model.2.Effect of EGCG on small intestinal morphology and barrier function of Bama xiang pigs under heat stressThe duodenal,jejunal and ileal tissues of pigs in each group were taken for the study of intestinal morphology and barrier function,and the results showed that:(1)Heat stress caused damage to the morphological structure of the small intestine of Bama xiang pigs,and also significantly reduced the height of the small intestinal villi and the villi-implicit ratio,while the addition of 0.05%EGCG helped to recover the morphological damage of the intestine and increased the height of villi and the villi occultation ratio.(2)Heat stress significantly increases the expression of HSP70 and HSP90 genes in the small intestine of Bama xiang pigs,indicating that high temperature causes a heat stress response in the small intestine of Bama pigs;Heat stress increased the expression of inflammatory cytokines TNF-α,IL-1β,IL-6,and IL-8 in the small intestine,increased the expression of TLR-4,and decreased the expression of intestinal tight junction proteins ZO-1,Claudin-3,Occludin,and Muc-2 genes.The addition of EGCG significantly reduced the expression of heat shock proteins,increased the expression of intestinal tight junction proteins and decreased the expression of TLR-4 in the small intestine,thereby alleviating heat stress-induced small intestinal mucosal injury and inflammatory response and improving intestinal barrier function,and the effect of 0.05% EGCG was superior to that of 0.025% EGCG.3.Effects of EGCG on colonic microbiota,short-chain fatty acids and TLR-4/NF-κB signaling pathway in Bama xiang pigs under heat-stressThe contents of the colon and the tissues of the colon of each group of pigs were taken and studied in terms of colonic microbiota,short-chain fatty acids and TLR-4/NF-κB signaling pathway,and the results showed that:(1)Heat stress significantly altered the microbial diversity and structure of the colon of Bama xiang pigs,significantly decreasing the abundance of Lactobacillus,Blautia,Holdemanella and Shuttleworthia,while significantly increasing the abundance of opportunistic pathogenic bacteria such as Clostridium＿sensu＿stricto＿1,which may be important in inducing an inflammatory response in the intestine.EGCG significantly increased the abundance of beneficial bacteria such as Lactobacillus,Blautia and Haldemanella in the colon of Bama xiang pigs under heat stress,while significantly reducing the abundance of unclassified＿c＿＿Clostridia,norank＿f＿＿norank＿o＿＿Clostridia＿vadin BB60＿group,and norank＿f＿＿norank＿o＿＿Izemoplasmatales and other opportunistic pathogenic bacteria in abundance,suggesting that EGCG can effectively alleviate heat stress-induced imbalance of intestinal flora and thus improve the intestinal microbial barrier function.(2)Heat stress significantly decreased the concentrations of acetic acid,propionic acid,butyric acid,isobutyric acid,valeric acid,isovaleric acid and hexanoic acid in the colon of Bama xiang pigs.EGCG significantly increased the concentration of acetic acid,propionic acid,butyric acid and isobutyric acid in the colon of Bama xiang pigs under heat stress,thereby improving the metabolism of the intestinal microflora.(3)Heat stress activated the TLR4/NF-κB signaling pathway in colonic tissues and significantly upregulated the expression of inflammatory genes MIP-1β,MIP-2,COX-2,and VCAM-1 downstream of this signaling pathway,while EGCG could effectively inhibit this signaling pathway and significantly reduce the expression levels of its downstream inflammatory genes.In summary,heat stress resulted in significantly reduced growth performance and severely impaired intestinal barrier function in Bama xiang pigs.EGCG improved growth performance and improved intestinal microflora and its metabolism by reducing the expression of heat shock proteins,TLR-4and inflammatory factors in the small intestine,increasing the expression of intestinal tight junction proteins in the small intestine,inhibiting the expression of TLR4/NF-κB signaling pathway and its downstream inflammatory genes in the colon,thereby alleviating heat stress-induced intestinal mucosal damage and inflammatory response,improving the intestinal barrier function of heat-stressed Bama pigs,and thus promoting intestinal health.The effect of0.05% EGCG was better than that of 0.025% EGCG,which provided a theoretical basis for the future development of EGCG as a feed additive that could improve the intestinal health of Bama xiang pigs under heat stress. |
