Impacts of High Temperatures, Heat Stress and Heat-Related Diseases in Pigs Raised Indoors

By Madonna Benjamin and Beth Ferry

Pork producers in Michigan and elsewhere have faced numerous challenges due to the increasingly hot weather over the past 50 years. Long-term weather forecasts for the Midwest U.S. and Michigan indicate that periods of sustained higher temperatures will occur more frequently and for more extended periods. It is predicted that Michigan will continue to experience higher numbers of storms.

For both humans and our livestock, high sustained temperatures, especially when combined with high humidity, can cause heat stress and the subsequent effects to reduce health. All mammals are at risk of heat stress when temperatures reach a certain threshold. Pigs are more heat-stress sensitive at lower temperatures, about 77 degrees Fahrenheit. In comparison, humans have a temperature threshold for heat stress at about 82 F.

Heat stress and pigs

Pigs are most comfortable and productive when environmental temperatures are within their thermal comfort range, the thermal neutral zone, which varies by age, size, moisture and wind speed. The impacts of heat stress on pig health and performance become greater as animals grow larger. Pigs have a lower threshold than other mammals because they lack sweat glands, which are required for evaporative cooling and their lungs are relatively small compared to their body size, limiting the effectiveness of panting in reducing body heat. Effects of higher temperatures and heat stress on sows, boars and finishing pigs, for example, begin to appear at about 70 F and become more serious with higher temperatures or humidity.

For these reasons, it is important that all pig farmers and their staff can recognize the signs of heat stress or improve the pigs' ability to dissipate heat during the summer months. Primarily, pigs will pant to remove excess heat and exhibit behaviors such as lying apart from other pigs and changing their dunging patterns to create a wallow for cooling. Be prepared to take additional adaptive actions that extend beyond barn ventilation and other structural features.