| A 2×2 factorial experiment with two ambient temperature levels(23,33℃) and two humidity levels(RH55%,80%)was conducted to study the effect of high ambient temperature and high humidity on the growth performance, redox state, stress level and immune function in growing pigs. This study investigated the mechanisms of the impacts of hot and humid environment on pig health and disease resistance, and provided basic date as early warning indicators and methods for the study of environmental stress of pig.Twenty-four crossed-bred ( Duroc×Landrace×Yorkshire ) barrows with an initial weight of 30±1.72kg, fitted with juguar catheter, were randomly assigned to four treatment with 6 replicates. The experiment lasted for 14 days. Blood samples were collected at day 1, 7, 14 to conduct indexes.The results showed that:(1)Temperature and humidity significantly affected growth performance, but no temperature×humidity interactions were found. In general, pigs subjected to high temperature had lower ADF(IP<0.01) and ADG(P<0.01)but greater F/G(P<0.01); pigs subjected to high humidity had lower ADG(P<0.01)but greater F/G(P<0.01).(2)Temperature significantly affected plasma redox state and erythrocyte antioxidant status, but no effect of humidity and temperature×humidity interactions were found. GSH and GSH / GSSG among heat stressed pigs was lowe(rP<0.05)at d 7 and 14. Regardless of humidity,erythrocyte SOD activity was greater(P<0.01)at d 1 but at lower(P<0.05)at d 14, GPX activity was lower (P<0.05)at d 7 and 14, CAT activity was lower(P<0.05)at d 14 and MDA concentration was greater at d 1,7 and 14 in heat stressed pigs.(3)Temperature significantly affected stress level and immune function, but no effect of humidity and temperature×humidity interactions were found. Regardless of humidity, plasma cortisol concentration was greater(P<0.01)at d 1 but lower(P<0.05)at d 7, total WBC was lower(P<0.05)at d 7, neutrophil and neutrophil to lymphocyte ratio was greater(P<0.05)at d 1, LPS-induced B-cell LPA was greater(P<0.05)at d 1 and d 7, CD4+ cells and CD4+/CD8+was lower(P<0.05)at d 14, IL-4 concentration was lower(P<0.05) at d 14, IFN-γconcentration was lower(P<0.01)but IL-4/IFN-γwas greater(P<0.05)at d 1,7,14 in pigs subjected to heat stress.According to these test results, high humidity was detrimental to the growth of pigs, but had no significant effect on health. Regardless of humidity, high temperatures were hazardous to the pigs, heat stress can lead to redox imbalance in the body, thus the formation of oxidative injury. During the early heat exposure period, pigs showed a higher stress level. The infulences of high temperature on the immune function of pigs differed according to the different duration of stress. Overall, B cell function enhanced at the beginning of the heat exposure, while T cell subsets disordered with the lasting of high temperature, and the immune function of pigs was reduced at last. High temperature can significantly improve the IL-4/IFN-γvalue, so shifting the Th1/Th2 balance, which occurred the phenomenon of immune elegant. Under heat stress, the imbalance of redox state and the immune system, disorder of regulatory factors may be important factors resulting in decreased animal disease resistance .
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