Beating the heat: Protecting pigs from heat stress
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EmailPractical nutritional and cooling strategies to safeguard swine health and performance during extreme temperatures.
Managing livestock health, productivity and welfare requires a clear understanding of seasonal variations and the impacts of extreme temperatures. Both hot and cold weather events can negatively affect growth, reproduction and mortality, so it is essential to implement mitigation strategies to reduce economic losses. Heat stress and the effects it has on swine have been documented in scientific literature for many years, with major themes continuing to be management strategies that address performance and alleviate welfare concerns.
The response to adapting to the onset of hot weather differs based on the animal’s previous exposure and tolerance level, genetics, lifecycle phase, and production stage. Pigs are exceedingly affected by heat stress because of the limited number of functional sweat glands and the thick layer of fat under the skin. When the animal experiences heat stress, it compensates for growth, feed efficiency and reproduction efficiencies to diminish the effect of heat stress (reference). As Michigan experiences its first heat wave in 2025, farmers will see signs of heat stress such as increased respiration rate, open-mouth breathing, lethargy and reduced feed intake. There is also a potential for increased morbidity and mortality when pigs cannot adapt and respond to heat stress.
Tools to predict heat stress in swine
As ambient temperatures increase with more intense heat events, this heat affects the animal’s ability to thermoregulate or to maintain a thermal neutral zone (TNZ) or the animals’ response required for homeostasis. To determine the potential for heat stress in swine, predictor tools such as TQA Weather Poster, Temperature Humidity Index and Heat Stress Index include warning index when handling or transporting swine. For example, when the humidity is 85%, temperatures are above 86 degrees Fahrenheit, it is considered dangerous to handle or transport hogs. At humidity above 90%, at the same temperature, you would only handle or transport hogs in an emergency.
A smartphone tool to predict heat stress in swine is an app, HotHog. Available in the Apple App Store and Google Play Store, HotHog links the local weather data to predict the heat stress levels of pigs.
Mechanical cooling systems
Direct cooling through increased airspeed. Elevated air speed increases airflow across the pig. This is accomplished through increasing ventilation, using stir fans, or use of naturally ventilated barns. Direct cooling is most effective when ambient temperatures are lower than the pig’s surface temperature (or less than 102.5 degrees Fahrenheit). A lower pen density allows pigs to spread out and increase airflow, thus cooling per animal.
Other systems include misters and foggers applied to the air, not directly to the animal, to cool the air. These systems have been shown to improve heat loss in non-sweating animals. Cooling systems at air inlets using evaporative pads or cooling cells have also been documented in recent studies to reduce temperature by 3.9 degrees Centigrade and had a cooling efficiency of 52%. There is a large variation in the effectiveness of these systems, depending on the size of the facility and mechanical system and the distance that the animals are housed from the system.
In a recent article, Iowa State University researchers highlight direct cooling systems that can be implemented in facilities. These include methods that combine the use of fogging, sprinklers, stir fans and high air velocity to directly wet the skin of the animals and induce pig comfort through convection, evaporation and conduction. Cool water can be applied first through fogging, followed by sprinklers or drippers onto the animal to assist with heat loss. These systems, in combination with high-speed air movement can help reduce heat stress and facilitate animal thermal comfort.
Environmental modifications
Additional environmental modifications can help reduce heat stress in animals housed outside and have full sun exposure. It is important that access to a shaded area is provided for the animals. Shading systems protect livestock from direct solar radiation and reduce heat transfer. Utilizing tree lines or artificial barriers, such as shade cloth are easy ways to mitigate direct sunlight onto the animals and buildings.
Nutritional strategies
Heat stress can reduce feed intake, thereby reducing access and absorption of essential protein or energy. Heat stress can damage the intestinal mucosa and reduce nutrient absorption. Effective strategies for alleviating heat stress include nutritional strategy options such as reducing the amount of crude protein levels in the feed from 12% to 10% and increasing the amino acid concentration. Additionally, when looking at nutritional adjustments to manage heat stress, there is support for decreasing the levels of fiber within the diet to help minimize the effects of heat stress.
The negative effects of heat stress on swine health, productivity and welfare are well-established, with the effects of heat stress on the productivity and welfare of animals being well-documented. As extreme heat events become more frequent, it is critical for farmers to implement effective mitigation strategies. Mechanical cooling technologies offer immediate relief and are widely adopted, while nutritional interventions require more time and careful planning. Ongoing evaluation of management practices and openness to new technologies will help producers safeguard the health and performance of their herds during periods of elevated temperatures and humidity.