Effect Of Early Lighting Time On Broiler Growth,Behavior And Cholesterol Metabolism After Hatching

Chickens are sensitiive to the change of light.Many animal physiological functions,such as growth and development,behavior and immune function,are affected by the light environment.The HPA axis is involved in regulating stress response,which regulates the secretion of Corticosterone also exhibit a certain rhythm.In addition to the HPA axis,brain cholesterol levels are also closely linked to animal behavior.Cholesterol is essential for the neurons.The content of cholesterol in the brain must be maintained in the correct range to ensure normal brain function.The lack of cholesterol in the brain is often associated with some degenerative neurological diseases.In this paper we first explored the effects of different lighting time on chicken behavioral patterns and cholesterol metabolism using local breeds such as yellow pheasants as experimental animals.We then selected a more representative Ross 308 broiler as an experimental animal and designed the experiment to use two different lighting times in the first week after the chicks were born,with the aim of exploring whether different lighting time during the critical growth period would have an effect on chicken behavior and cholesterol metabolism in the brain.1.Effects of lighting time during growth period on behavior and gene expression of Rugao Yellow ChickenOne-day-old chicks were divided into two groups and were reared under different photoperiods.Behavioral tests were conducted at 7 days of age.After the end of the test,blood was taken and brain tissue was collected.The results showed that the body weight and G/F of Rugao yellow chicken in LL group were remarkably higher than LD group chicken(P<0.01).Plasma biochemical parameters results,plasma creatine kinase(CK)and total cholesterol(T-chol)levels in LL group were higher than those in LD group(P<0.01).There was no significant change in Triglycerides(TG),High-density lipoprotein cholesterol(HDL-C),Low-density lipoprotein cholesterol(LDL-C),Aspartate aminotransferase(AST),Alanine aminotransferase(ALT),Free triiodide thyroid(FT3).Behavioral test results showed that Rugao yellow chicken exhibited better exercise ability and anti-stress ability under the light program of LD,and no depression-like performance.In addition,plasma melatonin levels in the LD group were also remarkably higher than those in the LL group(P<0.01).The expression of GR and 20HSD in the LD group of hippocampus decreased significantly(P<0.01);gene expression of 11?-HSD1 increased significantly(P<0.05);there was no significant change in the gene related to serotonin metabolism;in the group of LD,genes expression of 11?-HSD1 and 1?-HSD2 in the hypothalamus was remarkably increased(P<0.05),the 5-hydroxytryptamine metabolism-related gene 5-HTR1A was significantly decreased(P<0.05),and the expression levels of the genes NPY,AGRP and clock genes were remarkably higher(P<0.05).BSP results show that different light cycles make the promoter methylation rate of GR significantly changed.The above results indicate that different lighting time change the behavior of Rugao yellow chickens and affect the activity of the HPA axis.The change of photoperiod also affect the methylation rate in the promoter region and may further affect gene transcription.2.Effects of early lighting time after hatching on behavior and gene expression of Ross 308 broilerOne-day-old Ross 308 chicks were split into two groups.In the first week,two photoperiods(24L:0D;12L:12D)were used.In the second week,the 12L:12D lighting system was used to conduct behavioral tests at 7 days of age.After the end of the test,blood was taken and brain tissue was collected.The results showed no significant difference in body weight and G/F of Ross 308 broilers.The plasma creatine kinase(CK)and total cholesterol levels in the Ross 308 broiler in the LL group were significantly higher than those in the LD group(P<0.01).In the LL group plasma total cholesterol(T-chol),triglyceride(TG),high-density lipoprotein cholesterol(HDL-C)and aspartate aminotransferase(AST)were significantly higher than those of LD group(P<0.01).Behavioral test results showed that broilers under LD light show good behavioral patterns and have better anti-stress ability.Gene expression results showed that different light cycles had no significant effect on the expression of genes GR,MR and 1?-HSD1 in the hippocampus;the expression level of 1?-HSD2 in the hippocampus and the key enzyme for the synthesis of serotonin TPH1 in the LD group was significant increased(P<0.05);PER2 mRNA expression was remarkably higher(P<0.01).The expression of 11?-HSD1 and 20HSD in the hypothalamus of the LD group was significantly increased(P<0.05),genes expression of GR?5-HTR1A and MAO-A were remarkably decreased(P<0.01),the expression levels of TPH1 was significantly increased(P<0.05).TPH1 and clcok genes were remarkably increased(P<0.05).GR protein expression was remarkably decreased(P<0.05).The results show that the lighting time in key growth period after birth affects the behavior of the Ross 308 broiler,and the broiler shows a better behavior pattern in the LD light pattern.In the first week,continuous light was used to cause damage to the liver in the later period.Different lighting time after hatching may lead to changes in gene expression in the brain during late growth.3.Effect of early lighting time after hatching on hypothalamic and liver cholesterol metabolismOne-day-old Ross 308 chicks were split into two groups.In the first week,two photoperiods(24L:0D;12L:12D)were used.In the second week,the 12L:12D lighting system was used to conduct behavioral tests at 7 days of age.After the end of the test,brain and liver tissue were collected.Cholesterol levels in the hypothalamus were measured and key genes for cholesterol synthesis and breakdown in the brain and liver were detected using real-time PCR.Extraction of brain proteins Western blot was used to detect the expression of key proteins in cholesterol metabolism pathways in brain and liver.The results showed that the levels of cholesterol in the hypothalamus of the LD group was significantly higher than that of the LL group(P<0.05).The genes expression of SREBP1,SREBP2,HMGCR,LDLR and CYP46A1 in hypothalamus were all remarkablely increased.From the results of protein detection,we can see that the protein expression of SREBP1,SREBP2 and HMGCR in the hypothalamus of LD groups were significantly increased(P<0.05).At the same time,both CYP46A1 and CYP11A1 were also significantly increased(P<0.05).we examined the liver cholesterol levels of Ross 308 broilers and found that cholesterol level was significantly lower in the LD group than in the LL group(P<0.05).In the LD group,the genes related to cholesterol synthesis in the liver(SREBP1 and HMGCR)were significantly lower(P<0.05),and the expression of CYP27A1 that promoted cholesterol decomposition was significantly higher(P<0.05).The above results show that the LD light system significantly increases the content of cholesterol in the hypothalamus and reduces the content of cholesterol in the liver.We speculate that the LD light system may be more conducive to the development of brain neurons so that chicks have a good behavioral performance and low cholesterol content in the liver is conducive to the prevention of fatty liver.