| Heat stress refers to the sum of all kinds of reactions that animals and humans must make to protect their normal metabolism and various physiological mechanisms when the ambient temperature exceeds the comfortable temperature.With the global warming and greenhouse effect intensity,the farming mode has been seriously affected by heat stress,which has become one of the most important factors that affecting the development of poultry industry in China.Due to the physiological characteristics of high body temperature and lack of sweat glands in the skin of chicken,heat stress has a serious impact on the metabolic function of chicken.It’s reported that heat stress can lead to damage of internal tissue structure in chicken immune organs,so as to affect the birds’resistance to pathogenic microorganisms,and ultimately reducing the innate immunity.Heat stress can not only reduce growth performance parameters and immunity,but also can increase intestinal damage of broilers.However,the mechanisms of its action on intestinal immunity is still unclear.Therefore,in this study,a heat stress induced"susceptibility"model was established with broiler chickens to explore the mechanisms of pathogens infection under heat stress.First of all,the optimal conditions of immune injury induced by heat stress were determined by heat stress under different temperature conditions and different time.(1)Physiological changes of heat stressed chickens under different temperatures were detected.The chickens were randomly divided into four groups and treated at 37,39,41 and 43℃for48 h,respectively.The body temperature,respiratory rate,feather status and mental state of chickens were measured and recorded every 2 h.It was found that chicken feathers were disorderly,respiratory rate was accelerated and mental condition changes were appeared at 41℃.This temperature was selected as the experimental temperature for subsequent heat stress test.(2)The changes of immune-related factors were detected after different time of heat stress and different recovery time under 41℃heat stress,so as to determine the optimal time that 41℃heat stress affected the body’s immunity.The chickens were subjected to heat stress at 41℃for 0,6,12,18,24,30,36,42 and 48 h,respectively.The results showed that heat stress at 41°C could increase the proteins expressions of HSP70,IFN-α,IFN-βand IL-1β,and the response was most obvious at12 h of heat stress,and then these factors began to decrease.(3)The spleen proteins expressions of HSP70,IFN-α,IFN-βand IL-1βand organ indexes of spleen and liver were detected after 12 h of heat stress at 41℃,then recovery for 1,3,5,7,9,11 and 13d.After heat stress at 41℃for 12 h and recovery for 7 d,the immune function significantly decreased,including decreased indexes of spleen and liver,decreased spleen proteins expressions of IFN-αand IFN-β,and increased IL-1βprotein expression.Our results proved that broiler chickens heat stressed at 41℃for 12 h and recovered 7day resulted immune deficiency.Secondly,immune damage induced by heat stress reduces the body’s inherent protective mechanism and makes the body more susceptible to pathogens.Different intestinal bacteria infection after acute or chronic heat stress were used to explore the mechanisms of intestinal immune injury induced by heat stress in broilers.(1)We established a susceptible model of acute heat stressed chickens infected with Escherichia coli O157:H7 to explore the mechanism of acute heat stress on intestinal immune supreesion in chickens.The chickens in the heat stress+E.coli(HS+E.coli)group recovered for 7 days after 12 h stress at 41℃,and the chickens in the E.coli group and the HS+E.coli group were given with 1 m L E.coli O157:H7(1×10~9 CFU/m L)by oral administration,respectively.The chickens were killed by bloodlet on the 4th day after infection.Results showed that the intestinal length and weight of HS+E.coli group were higher than that of E.coli group,and the number of E.coli in cecal contents was higher than that of E.coli group.Heat stress can increase serum diamine oxidase(DAO)level and decrease Ig A level in chickens infected with E.coli.Heat stress had a protective effect on the morphology of small intestine except duodenum.Compared with E.coli group,the proteins levels of IL-1β,TNF-αand Caspase-1 in duodenum and ileum were significantly increased.Heat stress also significantly increased the gene and protein expressions of HSP70,TLR4 and NF-κB in duodenum and ileum.Heat stress did not affect the gene expression of HSP70,TLR4 and NF-κB in jejunum,but it inhibited the proteins expression of HSP70 and NF-κB.In addition,heat stress can decrease the expressions of IFN-β,IFN-γ,p-IRF3 and TBK1 in jejunum.The results showed that acute heat stress could amplify the effect of Escherichia coli on intestinal immune injury in broiler chickens by increasing TLR4-NF-κB/TBK1 signaling pathway.A susceptible animal model of chronic heat stressed broiler chickens infected with Salmonella Typhimurium was established to investigate the mechanism of chronic heat stress on intestinal immune function of broilers.Broilers aged 14 days were randomly divided into 4 groups,which were control group(Control),heat stress group(HS),Salmonella Typhimurium group(ST)and heat stress+Salmonella Typhimurium group(HS+ST).The chickens in the HS and the HS+ST group were subjected to heat stress at 35°C for two weeks with 8 h per day.After the heat stress,the chickens in the ST and the HS+ST group were orally given with 1m L ST(1×10~9 CFU/m L).The chickens were killed by bloodlet on the 4th day after infection.Results found that heat stress increased Ig A level in jejunum of chickens infected with ST.Heat stress significantly inhibited TNF-α,IL-6,IL-1β,NLRP3,Caspase-1,NF-κB-p65,p-NF-κB-p65,and TLR4-TBK1-related cytokines(interferon-α,interferon-γ,p-IRF3 and p-TBK1)in chickens infected with ST.Our results indicated that chronic heat stress can reduce the intestinal immune response of ST-infected chickens through inhibiting TLR4-NFκB-NLRP3 and TLR4-TBK1 signaling pathway.In conclusion,heat stress can regulate the intestinal immune response of broiler chickens infected with E.coli and Salmonella Typhimurium through TLR4-NF-κB/TBK1 signaling pathway. |
PDF Full Text Request