Effect Of High Ambient Temperature On The Intestinal Mucosa Barrier And Composition Of Ileal Microbiome Of Broilers

Heat stress is one of the most important stress on poultry production.Heat stress affects the intestinal mucosal barrier of poultry,which may be related to decrease feed intake,elevate body temperature or intestinal microbiome disorders.The present study aimed to examine the effect of high temperature on the ileal mucosal barrier and microbiome composition of broilers.The causes of high temperature affecting mucosal barrier and microbes in broilers were investigated.The relationship between mucosal damage and microbiom changes was analyzed.To provide a theoretical basis for relieving the effects of heat stress by nutrition measures to improved intestinal health.This paper are two part that short-term and long-term trials.144 male Arbor Acres broiler chicks were allocated to thermoneutral control(TC,21?)? high ambient temperature(HT,31?)and thermoneutral paired feed(PF,21?).The broilers had ad libitum access to feed and water in the HT and TC groups,and the feed intake in the PF group was paired with the HT group.The trial period lasted for 7days.Long-term high temperature trial: 96 male AA broilers at 21 days old were randomly divided into thermoneutral control(TC,21°C)and high ambient temperature(HT,31°C).The trial period is 28-49 days old.The results of the study as follows:1)Broiler's ADFI and ADG were significantly decreased,and F/G was significantly increased by both short-term and long-term high temperature treatments(P<0.05).ADG and F/G were significantly affected by high temperature under the same feed intake.2)Broiler's ileal villus height was significantly decreased,and the concentrations of LPS,TNF-? and CRP in serum was significantly increased by both short-term and long-term high temperature treatments(P<0.05);Short-term trial found that there was no significant difference in serum indexes among the three groups(P>0.05),which has indicated that the effect of high temperature on the intestinal mucosal integrity of broilers was at least partly related to the decrease in feed intake.3)Short-term high temperature significantly increased the mRNA expression of Occludin and ZO-1 in ileum mucosa(P<0.05).Long-term high temperature increased the mRNA expression of Occludin(P=0.074)and ZO-1(P=0.059);Long-term high temperature significantly the mRNA expression of increased mucosal MLCK(P = 0.005).4)Short-term high temperature significantly decreased the activity of ileal mucosal lysozyme(P<0.05).Long-term high temperature significantly increased the activity of ileal mucosal myeloperoxidase(P<0.001),significantly increased the mRNA expression levels of ileal mucosal IL-8(P< 0.001)and TNF-?(P< 0.001)in broilers,which has indicated that high temperature may induce a mild inflammatory response in the intestine.5)Broiler's species richness of ileal microbiome was significantly increased by both short-term and long-term high temperature treatments(sobs,Chao1,P<0.05).Short-term high temperature increased the trend of alpha diversity index of ileal microbes in broilers(shannon,P=0.066;simpson,P=0.128);there was no significant difference in species richness and diversity index of ileum broiler between the HT group and PF group(P>0.05),indicating that the effect of high temperature on the species richness and alpha diversity index of the microbiome was related to reduced feed intake.6)Broiler's beta diversity of microbiome was significantly influenced by both short-term and longterm high temperature treatments.There was no significant difference in ?-diversity between the HT group and the PF group(R=0.074,P=0.198),and the feed intake was significantly correlated with the PCoA primary coordinate 1 of the ileal microbes Unifrac distance(R=0.786,P<0.001).There was no significant correlation between body temperature?serum corticosterone with PCoA primary coordinate 1(P>0.05).These data indicated that the effect of high ambient temperature on the ileal microbes of broilers was mainly related to the decrease of feed intake.7)Broiler's composition of ileal microbiome was influenced by both short-term and long-term high temperature treatments.The relative abundance of the first dominant bacteria(Firmicutes,Lactobacillales and Lactobacillus)in the ileum of the HT group and the PF group was significantly lower than that of the TC group(P< 0.05),but there was no significant difference between the HT group and the PF group.At the same time,it was found that the feed intake was significantly correlated with the relative abundance of 30 genera in the ileum genus(TOP50),while the core temperature and serum corticosterone were significantly correlated with the abundance of some of the genus,indicating that the effect of high temperature on the composition of ileal microbiome in broilers is mainly related to the decrease of feed intake and less related to the direct effects of high temperature,such as body temperature or elevated corticosterone.8)Both short-term and long-term high-temperature trials has found that the relative abundance of main genus(TOP50)of ileal microbiome of broiler with serum LPS,TNF-? and CRP content,mucosal myeloperoxidase activity,IL-8,TNF-? and MLCK mRNA expression was significantly correlated,and only some genus were significantly associated with crypt depth,mucosal Occludin,ZO-1 and Mucin-2 mRNA expression,indicating that high temperature affects the composition of ileal microbiome,which may cause the changes of intestinal inflammation,and mucosal integrity,but have little effect on tight junction protein expression.The effect of high temperature on the ileal mucosal integrity of broilers was at least partly related to the decrease in feed intake.High temperature significantly increased species richness and affected the structure and composition of ileal microbiome,which was mainly related to the decrease of feed intake.High ambient temperature lead to ileal mucosal inflammatory response and activates MLCK,which may be one of the causes of impaired mucosal integrity.