| The egg-laying performance of laying hens is closely related to ovarian function,and the ovaries of laying hens at the end of laying begin to age naturally due to oxidative stress.Melatonin has antioxidant and anti-apoptotic effects.In order to study the relationship between the effect of melatonin on ovary and laying performance,550-day-old Hyline brown laying hens were fed a conventional basal diet as the control group,and fed a conventional basal diet supplemented with 1mg/kg melatonin as the melatonin group for 4 weeks.Using ELISA detection,fluorescence quantitative PCR,Western blot and transmission electron microscopy were used to detect hormones,receptors and proteins in blood and ovary of laying hens and analyze laying performance and egg quality.The effects of melatonin on ovary of laying hens at the end of laying period and its molecular mechanism were studied.The main results are as follows:1.Effects of feeding melatonin on production performance.The results showed that with the prolongation of feeding time,the laying rate of the control group gradually decreased from 77.99% to 76.73%,while the laying rate of the melatonin group remained at 77.50% to 78.60%.The number of atretic follicles in the melatonin group was significantly less than that in the control group.Tissue section observation showed that the granulosa cells in the control group were unevenly distributed and had more abnormal development,while the granulosa cells in the melatonin group developed normally It shows that feeding melatonin can maintain the normal development of the ovary of laying hens at the end of laying stage,and then maintain the egg production rate.2.Effects of feeding melatonin on ovarian development.The results showed that supplementation melatonin significantly up-regulated the relative expression levels of MT1 and LHR mRNA,down-regulated the relative expression levels of FSHR mRNA,promoted the relative expression levels of MT1,MT2 and LHR protein,inhibited the expression levels of FSHR protein,and significantly increased the contents of MT,LH and E2 in serum of melatonin group.Meanwhile,feeding melatonin can significantly up-regulate the mRNA expressions of antioxidant genes SOD2,GPX3 and Prdx3,and significantly increase the enzyme activities of antioxidant enzymes CAT,GSH-Px and SOD and T-AOC in the body,thereby reducing the body’s contents of ROS and MDA accumulated by oxidative stress.Detection of the transcription and protein expression levels of apoptotic factors in ovary showed that the expression of Bcl-2 mRNA and Bax and Caspase-3 mRNA were up-regulated by the addition of melatonin,and then down-regulated by the expression of Bcl-2 and Caspase-3 mRNA respectively.The transmission electron microscope was used to observe the ultrastructure of granulosa cells,and it was observed that melatonin could protect the organelles of granulosa cells and reduce the apoptosis of granulosa cells.These results indicate that feeding melatonin can regulate ovulation by regulating the transcription and expression of ovulation related hormone receptors,and then regulating the content of corresponding hormones,and at the same time improve the antioxidant ability of the body.By inhibiting the pro-apoptotic factor caspase-3 and decreasing the transcription and expression of Bax/Bcl-2,the ovarian apoptosis can be slowed down and the aging of the body can be delayed.3.Effects of melatonin on egg quality.The results showed that with the extension of feeding time,the average egg weight of the control group decreased from 63.98 g to 61.90 g,and the breaking rate increased from 1.68% to 2.70%.Compared with the control group,the average egg weight of melatonin group was maintained at 64.08 g,and the broken egg rate was maintained at about 1.62%.Meanwhile,the eggshell thickness,eggshell strength and calcium content of melatonin group were 0.098 mm,0.36 kg/cm~2 and 0.81% higher than those of control group.The results showed that melatonin could increase the calcium content of eggshell,increase the thickness and strength of eggshell,and decrease the rate of breaking egg.The results of this study show that melatonin increases the content of antioxidant enzymes by binding to its specific receptors MT1 and MT2,melatonin increased the relative expression level of antioxidant enzyme gene mRNA,reduced the levels of ROS and MDA,and reduced the oxidative stress caused by aging on ovary.Then melatonin inhibits apoptosis of ovarian cells by inhibiting the pro-apoptotic factor caspase-3 and decreasing the expression of Bax/Bcl-2 mRNA and protein,protects the growth of follicular granulosa cells and the function of organelles,and maintains follicular development,thereby promoting the mRNA and protein expression of LHR and inhibiting the mRNA and protein expression of FSHR.It can increase LH content,promote ovulation,delay ovarian senescence and maintain egg production rate.This study provides a theoretical basis for delaying ovarian senescence and prolonging the peak period of laying hens by melatonin. |
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