Reproductive integration of leptin and kisspeptin in small ruminants: Mechanisms, biomarker potential, and prospects for precision breeding.

Kisspeptin and leptin (LEP) are two essential proteins that play a central role in regulating reproductive hormones in small ruminants through the hypothalamic-pituitary-gonadal axis. These proteins influence the secretion of gonadotropin-releasing hormone, which, in turn, controls key hormones such as follicle-stimulating hormone and luteinizing hormone. Acting in synergy, kisspeptin and LEP also interact with other metabolic and reproductive signals, including insulin, estrogen, and neuropeptides, to coordinate reproductive function. Despite their importance, the detailed mechanisms by which these proteins operate, especially in relation to body condition score are not yet fully understood. This review explores their biological roles, interactions, and potential as markers for selecting high-performing livestock. External factors such as diet, stress, and seasonal changes can further influence their expression and activity. Understanding these pathways can support improved fertility management and the development of genetic or therapeutic strategies to enhance reproductive efficiency in goats and sheep.