Study On The Protective Effect Of Melatonin On Low Semen Quality In Dairy Goats Due To The High Temperatures In Summer

In recent years,the prolonged summer season and rising maximum temperatures have become one of the most important factors in livestock production causing heat stress in the testes of male animals,reducing semen quality,and causing various male reproductive diseases including male infertility.Dairy goats are heat-tolerant animals in semi-arid regions,and their physiological indicators are smoother than other mammals in the same hot environment,so we usually ignored the effect of heat stress on their male reproductive system.Melatonin is a neuroendocrine hormone with remarkable anti-inflammatory,antioxidant,and anti-apoptotic abilities,plays a direct physiological role in regulating sperm function and exhibits protection during testicular development and testosterone synthesis.Therefore,we speculate that melatonin may also have a few beneficial effects in heat stress-induced damage to the male reproductive system.This study aimed to determine the protective effect of melatonin on male reproduction during heat stress in dairy goats and to further explore its possible mechanisms and potential application in livestock production practices.We established a natural heat stress model using Saanen dairy goats,and then examined semen quality indicators using computer-assisted sperm analysis(CASA)for a complete spermatogenic cycle.Then we used histomorphological identification,immunofluorescence staining,and molecular biology techniques were used to assess the status of testicular tissue damage 7 days after heat stress;RNA-seq,Western blot,RT RNA-seq,Western blot,RT-q PCR,and bioinformatics analysis were used to explore the role and potential mechanisms of melatonin in alleviating heat stressinduced reproductive damage in dairy goats.The main findings of this study are as follows:1.Heat stress significantly damaged sperm structure and reduced dynamic parameters in dairy goats,and this heat damage had a certain lag and persistence,with subsequent effects beyond one spermatogenic cycle.Melatonin pretreatment significantly improved the reduction of sperm count and low semen quality in male dairy goats caused by heat stress and made semen quality back to the level of the Nature Control group more quickly.2.Heat stress caused structural damage to the testicular varicocele and reduced spermatogenic cells in dairy goats,and the apoptotic response was still significant 7 days after heat cessation.Melatonin pretreatment alleviated the heat damage to testicular tissue structure and significantly reduced the percentage of detached and detached varicocele.3.Heat stress mainly affected spermatocytes and round spermatocytes,while the number of spermatogonial stem cells and spindle spermatocytes did not change significantly.Melatonin pretreatment reduced the level of apoptosis of spermatocytes,and maintain the number of spermatocytes and round spermatocytes.4.Melatonin alleviated heat stress-induced spermatocyte and round spermatocyte apoptosis mainly by inhibiting PI3K/AKT and RAS signaling pathways.Melatonin pretreatment significantly downregulated the level of p-AKT,while the level of BCL-2 protein upregulated,then the ratio of BAX/BCL-2 decreased.5.The level of 17-methyltestosterone in serum was reduced and colony-stimulating factor CSF1 was infiltrated in the Heat Stress group,and melatonin could restore serum testosterone levels and alleviate local inflammatory responses in testes to some extent.6.The protective effect of melatonin on heat stress-induced testicular thermal injury was mainly dependent on melatonin receptor type 1B.In conclusion,this study systematically investigated the changes in semen quality,tissue structure,and spermatogenic cell damage under heat stress and evaluated the preventive and therapeutic effects of melatonin on heat stress-induced reproductive injury in dairy goats.The results suggest that melatonin can alleviate testicular and spermatogenic cell thermal damage and improve semen quality in male dairy goats.This study provides the theoretical basis and data support for exogenous melatonin use in production practice to prevent and control the adverse effects of summer heat on breeding and reproduction.