| In order to explore the effects of chronic heat stress on lipid metabolism of growing laying hens and the relieving effect of vitamin C,180 10-week-old Hyline brown laying hens with similar body weight(1.10±0.03 kg)were randomly divided into 3 experimental groups: Heat neutral control group(TN group,temperature 22±1℃),heat stress group(HS group,temperature 36±1℃ from 08:00 to 18:00 every day,and from 18:00 to 08:00 the next day,temperature 22±1℃),heat stress + dietary vitamin C supplement group(HSV group,diet supplemented with 300 mg/kg VC,The feeding amount,temperature control and heat stress groups were the same).Each experimental group had 6 replicates with 10 laying hens in each replicate group.The test period was 21 days.The samples were collected at the same time period on the 7th,14 th and 21 st day of the test,respectively,and the growth performance,blood biochemical indexes and liver metabolic function related indexes were determined.The results are as follows:(1)Compared with TN group,the average daily feed intake of HS group was lower,and the average body weight of HS group was significantly different(P<0.05).The average feed intake of HSV group was higher than that of HS group,and there was no significant difference in average body weight on days 7,14 and 21(P>0.05).(2)Compared with TN group,the contents of ALT,AST and TG in serum of HS group were significantly different(P < 0.05);Compared with HS group,serum AST and TG contents in HSV group were significantly different on day 7 and day 14(P < 0.05).(3)The tissue structure of the TN group was normal,and the cytoplasm was uniform and pink.In the HS group,there were obvious steatosis vacuoles in the cytoplasm of hepatocytes,fat accumulation in the liver tissue increased,and cell swelling occurred.Compared with HS group,HSV group showed clear structure of liver cells,reduced fat accumulation,and no inflammatory cell infiltration in hepatic lobules.(4)Compared with TN group,m RNA expression levels of AMPKα1,AMPKα2,PPARα and CPT1 in HS group were significantly decreased(P<0.05),while m RNA expression levels of ACC,HMGCR,GAPT,PPARγ and SREBF1 in HS group were significantly increased(P<0.05).Compared with HS group,m RNA expression levels of AMPKα1,AMPKα2,PPARα and CPT1 in HSV group were significantly increased(P<0.05),while m RNA expression levels of ACC,HMGCR,PPARγ and SREBF1 in HSV group were significantly decreased(P<0.05).(5)The results of liver metabolomics showed that 789 metabolites were identified in this study,and 173 differential metabolites were identified.Differential metabolites were mainly concentrated in cell component metabolism,energy material metabolism and amino acid metabolism.Conclusions:(1)Chronic heat stress significantly reduced the average feed intake and average body weight of laying hens,and caused oxidative stress damage such as steatosis,lipid deposition and cell structure change in liver cells of laying hens,and the changes of blood biochemical indexes of laying hens.(2)In chronic heat stress environment,dietary supplementation of VC can activate AMPK signaling pathway of laying hens,reduce abnormal lipid deposition in liver caused by chronic heat stress,and alleviate oxidative stress damage in liver;(3)The liver metabolites screened under chronic heat stress were mainly involved in the process of amino acid metabolism,and the change of liver metabolic pattern of laying hens under chronic heat stress was mainly manifested as increased protein decomposition. |
