| Environmental control in poultry housing is a key determinant in poultry production.As an important factor affecting the air environment in the poultry house,ammonia damages the respiratory tract mucosal barrier and immune function of poultry,causing detrimental effects to poultry health and production.The purpose of this study was to investigate the effects and mechanism of ammonia on the respiratory tract mucosal barrier of laying hens and to provide the theoretical basis for controlling the effect of ammonia exposure on laying hens production.The effect of acute ammonia exposure on respiratory tract mucosal barrier of laying hens was studied,and thereafter,the effect of ammonia combined with environmental humidity on the respiratory tract mucosal barrier injury of laying hens was determined.Experiment 1 Effects of acute ammonia exposure on respiratory tract mucosal barrier of laying hens.The experiment used 32 Hy-Line Brown layers at 30 weeks old.According to the concentration of ammonia,it was randomly divided into four treatment groups,0 mg/m3,30mg/m3,60 mg/m3 and 120 mg/m3,each of which was repeated for 8 times and exposed in the custom-made test chamber for 4 hours.Blood samples were collected.After cervical dislocation death,trachea and lung samples were fixed in tissue fixative and frozen in liquid nitrogen.The effect of different ammonia concentration on them was analyzed.The results showed that with the increase of ammonia concentration in the environment,the content of blood ammonia significantly increased and the content of Ig M significantly decreased（P<0.05）.Exposure to 120 mg/m3 NH3 significantly down-regulated the expression of Claudin-1in the lung（P<0.05）,and ammonia caused cilia lodging and adhesions in the respiratory tract,vascular congestion and edema in the lung.Also,exposure to 120 mg/m3 NH3 significantly up-regulated the expression of MUC5AC in the trachea and lung,and ammonia exposure significantly increased the content of mucin in BALF（P<0.05）.Ammonia exposure also increased the content of SIg A in BALF,and exposure to 60 and 120 mg/m3 NH3 significantly up-regulated the expression of SIg A in the trachea（P<0.05）.Ammonia exposure affected the expression of inflammatory factors.Exposure to 60 mg/m3 NH3 significantly up-regulated the expression of IL-10 in the trachea,while,120 mg/m3 NH3 significantly up-regulated the expression of TNF-αand IL-10 in the trachea（P<0.05）.Ammonia exposure activated the NF-κB pathway,since 60 mg/m3 NH3 significantly up-regulated the expression of I-KK-βand i NOS（P<0.05）,while 120 mg/m3 NH3 down-regulated the expression of I-κB-α,but up-regulated I-KK-βand i NOS expressions（P<0.05）.Experiment 2 Effects of ammonia and humidity on the respiratory tract mucosal barrier and production performance of laying hens.This experiment used 288 Hy-Line Brown layers at 53 weeks old.Birds were randomly divided into four groups according to ammonia concentration and relative humidity as follows;0 mg/m3NH3+55%RH,60 mg/m3NH3+55%RH,60 mg/m3NH3+75%RH and 60 mg/m3NH3+95%RH.The experiment was conducted for 6 weeks,and the production performance was assessed weekly.The egg quality was detected and blood,trachea,and lung samples were collected at the 3rd and 6th weeks of the experiment.The results showed that,At the same humidity,ammonia decreased the food intake and laying rate,increased the content of blood ammonia and uric acid,and decreased the total number of leukocytes.Also,ammonia exposure significantly down-regulated the expression of Claudin-1,Occludin,and ZO-1 in the trachea and lung（P<0.05）,leading to lodging,adhesion and loss of cilia,vascular congestion and edema in the lung.Exposure to 60 mg/m3 NH3 significantly increased the secretion of mucin in BALF,and the expression of MUC5AC,SIg A and p Ig R in the trachea and lung（P<0.05）.However,ammonia exposure significantly down-regulated the expression of IFN-γand IL-2 in Th1 cells,and up-regulated the expression of IL-4 and IL-10in Th2 cells（P<0.05）,indicating an imbalance between Th1 and Th2.Ammonia exposure significantly up-regulated the expression of pro-inflammatory factors TNF-αand IL-1β,activated NF-κB signaling pathway,and up-regulated the expression of pathway genes NF-κB,I-KK-β,COX2 and i NOS（P<0.05）.At the same humidity,with the increase of humidity,the food intake and the plasma Ig A content decreased,but the blood ammonia content and serum TNF-αwere increased significantly（P<0.05）.Higher humidity significantly decreased the expression of Occludin,Claudin-1,and ZO-1 in the trachea and lung（P<0.05）,resulting in the loss of cilia in the respiratory tract,hyperemia,edema,and accumulation of inflammatory cells in the pulmonary vessels.Humidity significantly increased the expression of MUC5AC and SIg A in the trachea and lung,and the secretion of SIg A and mucin in BALF（P<0.05）.With higher humidity,the expression of IFN-γand IL-2 were significantly down-regulated,IL-4 expression was up-regulated,and the imbalance of Th1 and Th2 caused respiratory tract inflammation.The expression of pro-inflammatory factors such as TNF-αand IL-1βwere significantly up-regulated,resulting in the down-regulation of NF-κB signaling pathway gene I-κB-αand up-regulation of NF-κB and i NOS（P<0.05）.In summary,ammonia exposure in the indoor environment damaged the respiratory tract mucosal barrier,induced Th1/Th2 cell imbalance and activated NF-κB signaling pathway,led to airway inflammation,caused their immune dysfunction.The findings suggest a dose-dependent effect,it was observed that the increase in environmental relative humidity aggravated the adverse effect of ammonia,and further reduced feed intake in poultry. |
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