Physiological consequences of heat stress in pigs

Heat stress negatively influences the global pork industry and undermines genetic, nutritional, management and pharmaceutical advances in management, feed and reproductive efficiency. Specifically, heat stress-induced economic losses result from poor sow performance, reduced and inconsistent growth, decreased carcass quality, mortality, morbidity, and processing issues caused by less rigid adipose tissue (also known as flimsy fat). When environmental conditions exceed the pig’s thermal neutral zone, nutrients are diverted from product synthesis (meat, fetus, milk) to body temperature maintenance thereby compromising efficiency. Unfortunately, genetic selection for both increased litter size and leaner phenotypes decreases pigs’ tolerance to heat, as enhanced fetal development and protein accretion results in increased basal heat production. Additionally, research has demonstrated that in utero heat stress negatively and permanently alters post-natal body temperature and body composition and both variables represent an underappreciated consequence of heat stress. Advances in management (i.e. cooling systems) have partially alleviated the negative impacts of heat stress, but productivity continues to decline during the warm summer months. The detrimental effects of heat stress on animal welfare and production will likely become more of an issue in regions most affected by continued predictions for climate change, with some models forecasting extreme summer conditions in key animal-producing areas of the globe. Therefore, heat stress is likely one of the primary factors limiting profitable animal protein production and will certainly continue to compromise food security (especially in emerging countries) and regionalise pork production in developed countries. Thus, there is an urgent need to have a better understanding of how heat stress reduces animal productivity. Defining the biology of how heat stress jeopardises animal performance is critical in developing approaches (genetic, managerial, nutritional and pharmaceutical) to ameliorate current production issues and improve animal wellbeing and performance.