Effect Of Probiotic On Intestinal Barrier Function Of Heat-stressed Broilers

This study was conducted to investigate the effects of dietary supplementation of probiotics on growth performance,serum biochemical parameters,intestinal mucosa morphology,intestinal innate immunity-associated gene expressions and caecum microflora of heat-stressed AA broilers,and to explore the potential underlying mechanisms by which the heat stress impairs the gut barrier fuction and the alleviating effects of probiotics.A total of 180 21-day-old AA broilers were randomly allotted to 3 groups with 4 replicates per group and 15 birds per replicate.The birds were housed in a temperature-controlled room at either 22±2 ? or daily cyclic high temperature 28?-35?-28?(heat stress treatment,HS)for 21 days.The birds were fed a corn-based basal diet(N)or the basal diet supplemented with 0(H)and 1.5 x 108 cfu/kg probiotics(H+L).On d 7 and 21 during the trial period,blood was collected for measurement of serum biochemical parameters.Segments(4 cm in length)from the midway part of duodenum,jejunum,ileum were harvested on ice bath for morphology assay,and ileum mucosa was immediately collected for tight junction protein and innate immunity-associated gene expressions assays.Mucosa and faeces from cecum were harvested for microflora analysis.The results showed as follows:1.Heat stress significantly decreased average daily feed intake(ADFI),average daily weight gain(ADG)and increased ADFI/ADG(1-21 d during the trial period).Dietary probiotics supplementation significantly enhanced average ADFI of heat-stressed birds as compared to heat-stressed birds fed basal diets.ADG and F/G in heat-stressed birds were not influenced by dietary probiotics supplementation(1-21 d during the trial period).Heat stress increased serum TNF-?(d 21)and IL-6(d 21)levels,and reduced the IL-10(d 21)levels of broilers fed basal diets.Dietary probiotics supplementation reduced serum TNF-?(d 21)and IL-6(d 21)levels and increased the IL-10(d 21),C-reactive protein(d 21)and TGF-?1(d 21)of heat-stressed birds as compared to heat-stressed birds fed basal diet.2.Heat stress significantly decreased duodenum villus height(V)(d 7 and 21),crypt depth(C)(d 21),V/C(d 7),increased duodenum V/C(d 21),ileal C(d 7).Dietary probiotics supplementation significantly increased duodenum V(d 7 and 21)and ileum V/C ratio(d 7),and incresed V in different level of heat-stressed birds as compared to heat-stressed birds fed basal diet.Heat stress decreased m RNA expressions of Claudin-1 and ZO-1 in ileum mucosa(d 7).Dietary probiotics supplementation increased m RNA expression of Occludin in ileum mucosa(d 21)of heat-stressed birds as compared to heat-stressed birds fed basal diet.Heat stress increased serum LPS(d 21),D-lactic acid(d 7)levels of broilers fed basel diets.Dietary probiotics supplementation reduced serum LPS(d 7 and 21)and D-lactic acid(d 7)levels of heat-stressed birds as compared to heat-stressed birds fed basal diet.3.Bacterial populations were similar in cecum mucosa and contents,but the OTU number and bacterial diversity was higher in mucosa than in contents.Heat stress increased bacterial abundance on d 7 and decreased bacterial abundance on d 21.Heat stress reduced the similarity of bacterial community in cecum.Heat stress was the main factor in influencing the cecum bacteria community,followed by dietary supplemental probiotics.Heat stress decreased proportions of Bacteroidetes and Bacteroides both in cecum mucosa and contents microbial community(d 7 and 21).Proportions of Cyanobacteria and Barnesiella in ceucm contents(d 7),and Desulfovibrio in ceucm mucosa(d 21)were decreased by heat stress.Increases inproportions of Tenericutes and Proteobacteria in ceucm mucosa(d 7 and 21),Actinobacteria in ceucm contents(d 7),as well as Synergistetes(d 7),Escherichia(d 7),Megamonas and Prevotella(d 21)in ceucm mucosa were observerd in heat-stressed broilers without probiotics supplementation.Dietary probiotics supplementation increased proportions of Bacteroidetes and Bacteroides(d 7 and 21),and decreased proportions of Proteobacteria,Synergistetes and Tenericutes in cecum mucosa.Increased proportion of Lentisphaerae in ceucm contents and proportion of Lactococcus in ceucm mucosa(d 7 and 21)were observed in heat-stressed birds fed diets supplemented with probiotics as compared to heat-stressed birds fed basal diet.4.Heat stress significantly decreased m RNA expression of TLR2(d 21),Av BD2(d 7 and 21)and Av BD12(d 21).m RNA expression of Av BD4 was significantly reduced by heat stress on d 7,while increased on d 21.Heat stress significantly decreased m RNA expression of COLEC10 in ileum.Dietary probiotics supplementation alleviated the upregulation of m RNA expressions of TLR4 and TLR5 induced by heat stress.Increased m RNA expressions of Av BD2(d 7)in ileum were observed in heat-stressed birds supplemented with probiotics as compared to heat-stressed birds fed basal diet.In conclusion,heat stress decreased growth performance,increased the levels of proinflammatory cytokines in blood,altered intestinal bacterial community and innate immunity-associated gene expressions,and damaged intestinal mucosa integrity.Dietary supplementation of probiotics can partially attenuate heat stress-induced intestinal barrier dysfunction in bacterial community and innate immunity-associated gene expressions and ameliorate the negative effects of heat stress on growth performance of broilers,and reduce the levels of proinflammatory cytokines and endotoxin in serum of heat-stressed broilers.