| Targeting the challenges of severe heat stress during summer and the controversial reports regarding immune barrier functions of poultry mucosa during heat exposure,the effects of long-term intermittent high temperature on specific immunity of mucosa(respiratory tract,digestive tract and reproductive tract)of growing pullets and laying hens were studied.It was necessary to lay a foundation for alleviating the immunosuppression of laying hens during heat stress at different production stages.The first experiment was to study the effect of intermittent high temperature on local mucosal specific immunity of growing pullets.A total of 144 60-day-old Hy-Line Brown young layers with similar body weight were randomly divided into 2 groups,6 replicates per group and 12 chickens per replicate.They were arranged and fed in two environmentally controlled chambers.The pre-trial period lasted for 14 days,and the feeding environment was maintained similarly for all chickens during these days.From the age of 74 days,the temperature of each room was set at 22°C and 35°C from 8:00 to 18:00 daily,and restored to22°C for the remaining hours.At the age of 104 days,Newcastle disease vaccine(ND)was administered.From the age of 74 days,samples were collected every 10 days,including blood,duodenum,lungs,fallopian tubes,etc.until 134 days old.The second experiment was to explore the effect of long-term intermittent high temperature on the local mucosal specific immunity of laying hens.A total of 144133-day-old Hy-Line Brown laying hens with similar body weight were randomly divided into 2 groups,6 replicates per group and 12 chickens per replicate,which were reared in two separate environmentally controlled chambers.Pre-test was conducted for 14 days,during which all chickens were managed under similar feeding environment.At 147 days old,the temperature of each room was set at 22°C and 35°C from 8:00 to 18:00 every day,and 22°C for other time.At the age of 177 days,Newcastle disease vaccine was given.From 147 days old,samples were collected every 10 days,including blood,duodenum,lung,fallopian tube,etc.until 207 days old.The results showed that the responses of growing pullets and laying hens to long-term intermittent high temperature were similar.From the 10th day after intermittent temperature treatment to the end of the experiment,the production performance(including food intake,body weight,tibia length of growing pullets,egg weight and egg laying rate of laying hens),immune organ index(spleen proportion),humoral immune function(including ND antibody titer,IgG and IgM concentration),cellular immune function(including CD4~+and CD8~+T-lymphocyte ratio,T-lymphocyte activity in peripheral blood),and local mucosal immunity including ND antibody titer and secretory IgA(sIgA)level of duodenum,lung and fallopian tube mucosa decreased significantly(P<0.05),and the gene expression of inflammatory factors(including IL-6,TLR-4,iNOS,TNF-αand IFN-γ)in spleen increased significantly(P<0.05).sIgA synthesis and secretory related genes expression in duodenum,lung and tubal mucosa were significantly inhibited(P<0.05)during long term intermittent hyperthermia.These included MHCII and TCR in T-cell-dependent pathway,MyD88,TACI and iNOS in T-cell-independent pathway and other related genes such as TGFβ1,pIgR,TRAF6,IL-6,TLR-4.After given Newcastle disease vaccine 10-30 days,the titer of ND antibody of duodenum,lung and fallopian tube mucosa in the controlled temperature group was significantly higher than that in high temperature group(P<0.05),while no significant changes were observed in the high temperature group(P>0.05).With the extension of treatment time,the difference between normal temperature group and high temperature group was stable of growing pullets,while for laying hens,the difference between normal temperature group and high temperature group was increasing.The above results showed that the long-term intermittent high temperature continued to reduce the production performance,humoral immune function,cellular immune function and local mucosal immunity,and slowed down the development of immune organs.It inhibited the synthesis and secretion of IgA in digestive tract,respiratory tract and reproductive tract by reducing the expression of genes related to T-cell-dependent pathway and non-T-cell-dependent pathway.Compared with growing pullets,the long-term intermittent high temperature had more severe damages to the mucosal immune barrier function of laying hens. |
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