Effects Of Melatonin On Synchronous Ovulation And Timed Insemination Artificial In Heifers

Ovsynch and timed Artificial Insemination(OTAI),as an efficient and rapid reproduction technology,has gradually occupied an important position in animal husbandry production.The technology is currently mainly applied to dairy cows,but the research on beef cattle is relatively few,and the pregnancy rate is low,so there is still a lot of research space.Melatonin is a strong and effective antioxidant in the body.It can directly remove intracellular free radicals,increase the activity of antioxidant enzymes,reduce the production of free radicals,improve the quality of oocytes and granulosa cells,and further affect the size and quality of the corpus luteum,thus increasing progesterone concentration,maintaining cow pregnancy,and increasing conception rate.In this experiment,86 healthy and moderately fat young Simmental cattle were randomly divided into four groups:control group(CTR),one melatonin(MT)group,one melatonin+human chorionic gonadotropin(HCG)group and two melatonin groups(2MT).10 cows were randomly selected from each group,and blood samples were taken before and after two melatonin injections to detect serum malondialdehyde(MDA),superoxide dismutase(SOD),and glutathione peroxidase(GSH-P_X)and catalase(CAT)levels.Blood samples were collected on the 10th and 45th day after artificial insemination.Progesterone levels were measured,and the conception rate was determined 60 days after artificial insemination,with the purpose to screen out the technical solutions for improving the timing of fertilization in heifer during the same period of ovulation.The results showed that the pregnancy rate of the heifer melatonin group was significantly higher than that of the control group and melatonin+HCG group(CTR vs 2 MT,P=0.036;MT+HCG vs 2 MT,P=0.017),and difference was not significant compared with the MT group(P=0.053).The serum progesterone concentration was measured on the 10th day and the 45th day after artificial insemination.The progesterone level in the melatonin+HCG group was significantly higher than that in the control group and the MT group(P<0.05),and the difference was not significant compared with the 2MT group.(P>0.05).There was no significant difference in MDA,SOD,GSH-P_X and CAT concentration between the groups before the first melatonin treatment(P>0.05).After melatonin treatment for 24 h,the MDA content of MT group was compared with the control group.The levels of antioxidant enzymes SOD and GSH-P_X significantly increased(P<0.05),and the difference of CAT concentration was not significant(P>0.05).The difference of MDA,SOD,GSH-P_X and CAT concentration before the second melatonin treatment was not significant(P>0.05).After melatonin treatment for 24 h,the MDA concentration of the 2MT group was significantly higher than that of the other three groups.The levels of antioxidant enzymes SOD and GSH-P_X significantly increased(P<0.05),and the difference of CAT concentration was not significant(P>0.05).The research results indicate that melatonin treatment can improve the antioxidant level of heifer,and two melatonin can significantly increase the conception rate of heifer during the same period of ovulation.Although HCG can increase progesterone levels,it can not improve the conception rate.