Effects Of Ambient Temperature And Humidity On Growth Performance,Oxidative Status Of Growing Peking Ducks And Its Regulating Mechanism

Two experiments were conducted in this study to investigate the effects of ambient temperature on the growth performance,carcass traits,blood parameters and oxidative status of Peking ducks,as well as the effects of temperature on intestinal development,HSPs,antioxidase gene expression of Peking ducks under different humidity conditions.We aimed to determine the relationship between temperature and humidity and to screen biochemical and molecular indicators reflecting heat stress of Peking ducks.We further explored the regulation mechanism of oxidative damage caused by high temperature.Our objective was to provide a theoretical basis for the temperature control of ducks.Experiment 1 was carried out to investigate the effects of ambient temperature on the growth performance,carcass traits,blood parameters and oxidative status of growing Peking ducks.A total of21614-d-old male White Pekin ducks were allocated randomly to 6 environment-controlled chambers with ambient temperature set at 20,22,24,26,28,and 30°C from 14 to 42 days of age,respectively,the relative humidity of all treatment groups were set to 60%.The results showed that with the increase of ambient temperature,the body weight,daily weight gain,feed intake,breast meat weight,leg meat weight and abdominal fat weight all showed a decreasing trend.According to broken-line regression,the upper critical temperature for the growth performance of the Peking ducks should be lower than27?,while for the carcass traits the upper critical temperature should be lower than 26?.The meat color L^*value of the breast meat of Peking ducks increased significantly?P<0.05?,but the a^*value decreased significantly?P<0.05?at 30?.Under high temperature conditions,the levels of plasma T₃,total protein,uric acid,albumin,total triglyceride,total plasma bilirubin,aspartate aminotransferase,?-hydroxybutyrate dehydrogenase and lactate dehydrogenase were significantly reduced?P<0.05?,while the corticosterone levels increased significantly?P<0.05?.High temperature significantly reduced Peking duck red blood cell count,hematocrit,hemoglobin,white blood cell count,and platelet count?P<0.05?.Under high temperature conditions,the plasma and liver GSH-Px activities of Peking duck were significantly reduced?P<0.05?,while the MDA level was significantly increased?P<0.05?.Experiment 1 was carried out to investigate the effects of ambient temperature at different humidity on the growth and carcass traits,intestinal development,core temperature,and antioxidant enzyme gene expression of growing Peking ducks.There were 6 treatment groups,and the temperature and humidity of the environment were set to 20?+60%,25?+60%,30?+60%,20?+80%,25?+80%,30?+80%,respectively.180 14-day-old male Peking ducks with basically the same weight were randomly divided into 6 treatments,each treatment with 6 repeats and 5 ducks per repeat,ducks were reared at environment-controlled chambers and the experienment lasted 28 days.The results showed that the ammonia level in the house increased at 20?.With the increase of the ambient temperature,the core temperature of the Pekin duck increased,while the humidity had no significant effect on the core temperature of Peking duck under 30?.However,the ambient temperature had no significant effect on the shearing force,drip loss,and pH?P>0.05?.The the main effect analysis showed that when the ambient humidity increased from 60%to 80%,the daily gain of Peking ducks decreased significantly?P<0.05?,and the feed-weight ratio and abdominal fat percentage increased significantly?P<0.05?.At the same time,temperature and humidity had a significant interaction effect on the daily weight gain and breast meat rate of Peking ducks?P<0.05?,the relative humidity increased from 60%to 80%significantly reduced the daily weight gain of 14-42-day-old Peking ducks at 20?and 30??P<0.05?,while the relative humidity had no significant effects on the daily weight gain at 25??P>0.05?.In addition,the body weight,daily weight gain and feed intake of Peking ducks were further reduced with the increase of humidity at 30??P<0.05?.The length and weight of the small intestine decreased significantly at 30??P<0.05?.Under high temperature and high humidity conditions,HSP90 mRNA in liver,ileal mucosa and feathers were significantly increased?P<0.05?.The gene expression of Nrf2,SOD2 and CAT in the liver were significantly increased at 30??P<0.05?.In summary,the high temperature and high relative humidity significantly reduced the growth of growing Peking ducks and high humidity could aggravate the growth depression caused by high temperature.The upper critical temperature to keep optimal growth performance should be below 27?and the upper critical temperature to keep optimal breast meat yield should be below 26?.Plasma Triiodothyronine and corticosterone was sensitive blood indicators for duck heat stress and HSP 90mRNA was sensitive molecular indicator for duck heat stress.High temperature could lead to lipid peroxidation damage and the regulatory mechanism of ducks responding to it was related to significant increasing expression of antioxidant enzyme genes such as SOD2 and CAT and the nuclear transcription factor Nrf2 under high temperature conditions.