| Estrus Synchronization plays an important role in the development of the beef cattle industry.During the synchronous estrus processing,the development of bovine follicles is susceptible to variation in reactive oxygen species and short-term hormones,resulting impaired in oocyte development and leading to a decline in the rate of estrus and conception during estrus.Melatonin（MT）present in various tissues and organs of mammals,plays a role in various physiological regulation.More and more studies have shown that MT can improve the reproductive performance of female animals and the reproductive efficiency of female animals in actual production.However,there are few reports on the research and application of MT to estrus synchronization in beef cattle.This paper mainly studied the metabolism of exogenous MT in beef cattle,the effects of subcutaneous injection of MT on plasma antioxidant levels and reproductive hormones during twice PG treatment,as well as the effects of MT on synchronous estrus rate and estrus conception rate.In this study,twelve beef catties were randomly divided into four groups,at 8 o’clock in the morning,0 mg,0.464 mg,4.64 mg and 46.4 mg melatonin were injected and measuring the concentration of melatonin at different time pionts;eighty beef catties were randomly divided into four groups,during period of the second injection and artificial insemination in the treatment,melatonin of 0 mg,0.464 mg,4.64 mg or 46.4 mg was injected,and collecting blood for the determination of plasma antioxidant level and reproductive hormone content.Statistical estrus rate and conception rate.The following research results were obtained:1.After subcutaneous injection of different doses of MT into beef cattle,the concentration of MT in plasma was at a high value in 0.5 h,which was significantly higher than that of the control group（P<0.01）,and then showed a downward trend.0.464 mg MT was injected and metabolized to normal levels after 8 hours,while 4.64 mg or 46.4 mg MT was metabolized to normal levels after 14 hours.The metabolic rate of MT in beef cattle increases with increasing concentration,and decreased with increasing time after injection.2.Subcutaneous injection of 4.64 mg or 46.4 mg MT could significantly reduce the content of MDA in plasma during twice MT injections（P<0.05）,significantly increase the content of GSH-Px（P<0.05）,and significantly increase the content of SOD（P<0.01）.4.64mg MT could significantly increase the content of CAT;46.4 mg MT significantly increased the plasma concentrations of FSH and LH during breeding（P<0.05）,4.64 mg MT significantly increased the plasma concentration of FSH and E2 during breeding（P<0.05）,and the plasma P4 value was significantly increased on the 7th day after breeding（P<0.05）.3.During the estrus synchronization treatment,subcutaneous injection of 46.4 mg MT significantly increased the estrus rate of beef cattle（95.00%vs 70.00%;P<0.05）,and the estrus conception rate was higher than that of the control group,but there was no difference（73.68%vs 42.85%;P>0.05）.In conclusion,exogenous melatonin can enhance the estrus rate and conception rate during estrus by improving the body’s antioxidant level and changing the concentration of reproductive hormones.The injection of 46.4 mg of melatonin has the best effect. |
