Physical environment and thermotolerance in ruminants: An updated review on strategies for controlling heat stress

Abstract

Heat stress is among the main environmental challenges limiting the efficiency, welfare, and sustainability of ruminant production systems worldwide. Rising ambient temperature, humidity, and solar radiation and reduced nocturnal cooling intensify thermal load and impair the ability of animals to maintain homeothermy. This review summarizes the biological mechanisms of heat stress and evaluates the effectiveness of environmental mitigation strategies for cattle, sheep, and goats. Thermal challenge triggers coordinated physiological responses, including increased respiration rates, peripheral vasodilation, altered endocrine activity, reduced feed intake, oxidative stress, immune dysfunction, and changes in rumen metabolism. When exposure is prolonged, these responses are associated with lower milk yield, reduced growth, impaired reproductive performance, and increased health risk. The severity of impacts depends on the species, breed, production level, acclimation capacity, and housing conditions. Management interventions such as natural or artificial shade, mechanical ventilation, sprinklers, evaporative cooling, improved water access, and climate-responsive housing can substantially reduce heat load and improve productive resilience. However, their efficiency varies according to the climatic region, farm scale, and resource availability. Integrating infrastructure, management, nutrition, and genetic selection for thermotolerance is likely to provide the most sustainable long-term solution. As climate variability increases, heat-stress mitigation should be considered a strategic priority for profitable and welfare-oriented ruminant production.