The buck effect in goats: A review of neuroendocrine mechanisms, modulating factors, and applications in reproductive management

The male effect (buck effect) is a sustainable, hormone-free biostimulation strategy in caprine reproduction, in which introducing sexually active bucks to seasonally anestrous does increases luteinizing hormone (LH) pulse frequency, thereby stimulating folliculogenesis and ovulation. This review provides a comprehensive synthesis of the sensory, neuroendocrine, breed-related, and management factors governing male biostimulation in goats (Capra hircus). Olfactory signals, including the identified primer pheromone 4-ethyloctanal, are perceived through the main and accessory olfactory systems and act together with visual, auditory, and tactile cues. These sensory inputs activate the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator probably through the medial amygdala and the arcuate kisspeptin/neurokinin B/dynorphin (KNDy) neuronal network; the resulting rise in estradiol may subsequently trigger a preovulatory LH surge. The response is strongly modulated by photoperiod and latitude, buck libido, female body condition, breed-specific anestrous depth, and climatic stressors, particularly in tropical production systems. To optimize outcomes, practical management frameworks now integrate artificial photoperiod treatments of bucks, social facilitation protocols, such as the buck-to-buck effect, targeted nutritional supplementation, and fixed-time artificial insemination. Emerging tools such as synthetic buck odor and crude pheromone extracts show potential for non-contact reproductive control but still require validation of their ovulatory efficacy during anestrus. Overall, male biostimulation links sensory biology with practical herd management and represents a promising hormone-free alternative to exogenous hormonal treatments, consistent with growing demands for animal welfare and sustainable livestock production.