15 The Trusted Source for Canada’s Pork Producers Better Pork | June 2024 Heat Stress Heat stress is no longer an issue limited to tropical regions; countries in temperate regions are also experiencing hotter than usual summer months. In Canada, the warm summer months increase the ambient temperature inside pig barns. When the ambient temperature within pig barns rises above 25 C, pigs will start to experience heat stress (Figure 1). However, ambient temperature is not the only factor that causes heat stress; the relative humidity in the barn can also contribute, such that lower temperatures with high relative humidity can still have a large impact (Figure 1). Why are pigs sensitive to heat stress? Pigs do not sweat well. They have few sweat glands and their skin insulation impedes sensible heat loss, due to its thick subcutaneous fat depth. These factors, coupled with their high basal metabolic heat production and high lean tissue gain (due to intense genetic selection), make pigs particularly sensitive to heat stress, compared to other livestock animals. How do pigs respond to heat stress and what are the consequences? Pigs respond to heat stress through complex physiological and behavioural mechanisms, which have negative consequences for productive efficiency and health (Figure 2). Heat-stressed pigs are less active and reduce their feed intake to reduce metabolic heat production and maintain body temperature. This reduction in feed intake results in reduced growth and feed efficiency. The physiological adjustments to heat stress can disturb the antioxidant status and cell funcHeat stress emergency Heat stress danger Heat stress alert No heat stress 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% Room temp. 35°C 34°C 33°C 32°C 31°C 30°C 29°C 28°C 27°C 26°C 25°C 24°C 23°C 22°C 21°C Relative humidity Figure 1. Heat stress index for grow-finish pigs (Xin and Harmon, 1998)
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