Effects Of Heat Stress On Growth Performance,Fat Deposition And Liver Anti-Oxidative Capacity In Broilers

Heat stress is the main environmental stress in modern poultry breeding industry.The intensive and large-scale breeding mode and the change of air temperature lead to frequent heat stress in poultry breeding.The excessive deposition of fat in broiler,especially the excessive deposition of abdominal fat caused by heat stress,has become a prominent problem in poultry breeding,which reduces the economic characters and economic benefits of poultry,and seriously affects the development of poultry breeding industry,the resulting slaughter waste can also seriously pollute the environment.In this study,Arbor Acres(AA)broilers were taken as the research object to explore the effects and mechanism of heat stress on growth performance,fat deposition and liver antioxidation in broilers,in order to provide theoretical basis and ideas for how to prevent and alleviate heat stress injury in poultry breeding.Experiment 1: Effect of heat stress on growth performance of broilers.Ninety-six broilers were randomly divided into two groups.One group was suitable temperature control group(TN group,28 ℃),and the other group was cyclic high-temperature group(HS group,35 ℃ from 7:00 to 19:00;28 ℃ from 19:00 to 7:00).Each group had 6replicate cages with 8 chickens per replicate.The broilers were treated with heat stress from 14 days to 35 days old,and the growth performance of broilers was measured at the end of the experiment.The results showed that: Heat stress significantly decreased the final body weight,average daily gain and average daily feed intake of broilers(P < 0.05),and increased the ratio of feed to feed,but the difference was not significant(P > 0.05).The above results suggest that under the condition of heat stress,the growth performance of broilers was inhibited,and the feed utilization rate decreased,which decreased the broiler breeding efficiency and increased the breeding cost at the same time.Experiment 2: Effect of heat stress on fat deposition and liver antioxidant capacity in broilers.The design of the experiment is the same as that of experiment 1.At the end of the experiment,the intermuscular fat content,abdominal fat rate,liver antioxidant enzyme activity,fat deposition and liver antioxidant related gene expression were measured.The results showed that:(1)Heat stress significantly increased intramuscular fat content in breast muscle,intramuscular fat content in leg muscle and abdominal fat rate in broilers(P < 0.05).(2)Heat stress significantly decreased the activities of antioxidant enzymes(SOD and GSH-Px)and increased the content of malondialdehyde(MDA)in liver(P < 0.05).(3)Heat stress significantly down-regulated the expression of liver antioxidant-related genes(Nrf2),and significantly up-regulated the expressions of inflammation-related genes(NF-κB and LITAF)and fat synthesis-related genes(FAS and SREBP1)(P < 0.05).The above results suggest that heat stress may promote fat synthesis and transport by up-regulating the expression of genes related to fat synthesis in the liver,and by reducing the antioxidant capacity of the liver and up-regulating the expression of inflammation-related factors.it triggers oxidative stress and inflammation in the liver,which in turn promotes fat deposition.To sum up,heat stress reduced the production performance and liver antioxidant performance of Arbor Acres broilers,promoted fat deposition,and seriously affected the breeding efficiency of broilers.