Role of Heavy Metal Poisoning in Modulating Reproduction Rates in Sheep

Objective: Heavy metal contamination is an increasing environmental concern with significant implications for livestock productivity. This study aimed to evaluate the role of lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), and nickel (Ni) exposure in modulating reproductive performance in sheep, with emphasis on hormonal alterations, gametogenic impairment, and fertility outcomes. Method: A structured literature-based synthesis was conducted using peer-reviewed studies published between ۲۰۱۰ and ۲۰۲۵. Major scientific databases were searched to identify experimental and field studies investigating heavy metal exposure exclusively in sheep. Inclusion criteria required quantifiable reproductive outcomes such as testosterone, FSH, LH, sperm parameters, ovarian follicle count, abortion rate, or lambing performance. Data were extracted and analyzed descriptively due to heterogeneity in exposure models and outcome reporting. Results: Ten eligible studies were included. Chronic environmental exposure to Pb, Cd, Cr, and Ni was consistently associated with significant reproductive impairment. In heavily exposed rams, serum testosterone levels declined by up to ۹۲%, accompanied by reduced sperm concentration, increased abnormal sperm morphology, and testicular histopathological damage. Prenatal exposure to metal-contaminated environments reduced ovarian follicle reserves in female fetuses and increased the incidence of reproductive dysfunction. In vitro exposure of ovine oocytes to Cd resulted in a marked decline in mitochondrial integrity (from approximately ۵۲% to ۸%). Field studies further reported increased abortion rates and reduced fertility indices in contaminated grazing regions. Conclusion: Evidence indicates that heavy metal exposure significantly disrupts endocrine function and gametogenesis in sheep, leading to measurable declines in reproductive performance. Environmental monitoring and mitigation strategies are essential to protect flock fertility and livestock productivity.

کلیدواژه ها:

Heavy Metal ، Sheep ، Reproduction toxicity