Seasonal Infertility in Swine under Tropical Conditions: Pathophysiological Mechanisms, Reproductive Consequences and Mitigation Strategies

Abstract

Seasonal infertility is a multifactorial reproductive disorder that reduces reproductive efficiency in swine, particularly under tropical and subtropical production conditions. This review examines the pathophysiological mechanisms, reproductive consequences and mitigation strategies associated with seasonal infertility, with emphasis on heat stress under Indian conditions. Elevated ambient temperature, high relative humidity and long photoperiods disrupt normal reproductive physiology by impairing endocrine regulation, metabolic homeostasis, oxidative balance and cellular function. Heat stress suppresses feed intake and contributes to negative energy balance, altered hypothalamic-pituitary-ovarian activity, reduced gonadotropin secretion and impaired ovarian steroidogenesis. These changes compromise follicular development, oocyte competence, ovulation, luteal function, embryo survival and litter size. In boars, elevated temperature impairs spermatogenesis, semen quality, testosterone synthesis and fertilising capacity, thereby contributing further to seasonal reproductive losses. The review also summarises the major consequences for herd performance, including delayed puberty, prolonged weaning-to-oestrus intervals, reduced conception and farrowing rates, increased embryonic loss and smaller litters. Under Indian smallholder and semi-intensive systems, limited environmental control, inadequate housing, high temperature-humidity index conditions, disease pressure and seasonal feed and water constraints may intensify these effects. Management approaches include improved shade, ventilation, sprinkling or wallowing facilities, continuous access to clean drinking water, strategic feeding, antioxidant supplementation, timely oestrus detection, appropriate hormonal interventions, routine semen evaluation and herd health management. Long-term responses may include selection for heat-tolerant genotypes and the use of precision livestock farming, genomic tools and reproductive biotechnologies. Overall, seasonal infertility in swine reflects the interaction of environmental stressors with endocrine, metabolic and cellular pathways. Integrated, context-specific mitigation strategies are therefore required to support reproductive resilience and improve productivity in tropical production systems.