The common belief that pigs do not sweat is largely accurate, yet it oversimplifies the biological reality of porcine thermoregulation. Pigs are warm-blooded and must actively manage their internal temperature to survive. They possess sweat glands, but these glands are ineffective for cooling the body mass. This forces the animals to rely on alternative, less efficient behavioral and respiratory strategies to dissipate heat, making them particularly vulnerable to high temperatures.
The Anatomy of Porcine Sweat Glands
Pigs do have sweat glands, but their structure and distribution render them ineffective for whole-body cooling. The majority of the skin surface contains apocrine sweat glands. These glands typically secrete an oily, viscous substance into the hair follicle, which is designed for scent marking, not evaporative cooling.
The eccrine gland, responsible for effective cooling in humans, is present only in a very limited distribution on the pig’s body. Functional eccrine glands are primarily restricted to the snout and the carpal regions. This surface area is insufficient to cool the animal’s substantial body mass. Since the glands cannot produce enough watery sweat across a wide surface area, pigs cannot utilize the efficient evaporative cooling that humans and horses rely on.
Primary Cooling Strategy: The Importance of Wallowing
Since sweating is ineffective, wallowing in mud or water becomes the pig’s primary behavioral strategy for thermoregulation. This instinctual behavior directly addresses the lack of functional sweat glands by artificially wetting the skin surface. The action of submerging and coating the skin facilitates heat transfer through two main scientific principles: conduction and evaporation.
When a pig lies in cool mud or water, heat transfers directly from the warmer body to the cooler substrate via conduction. This is followed by the sustained cooling effect that occurs as the water or mud layer begins to dry. The evaporation of this external moisture draws heat away from the pig’s skin, effectively mimicking the cooling process of functional sweating.
The dried mud layer offers secondary benefits, acting as a sunscreen to protect the skin from solar radiation. Wallowing is fundamental, and pigs prefer mud over water, as mud stays wet longer, prolonging the evaporative cooling effect.
Evaporative Cooling Through Respiration
When behavioral strategies like wallowing are unavailable, the pig must rely on internal physiological processes, primarily evaporative cooling through respiration. This is accomplished through rapid, shallow breathing, a process scientifically known as thermal polypnea or panting. By increasing the respiration rate, the pig enhances the evaporation of water from the moist surfaces of its respiratory tract, including the tongue, nasal passages, and lungs.
This increase in breathing rate significantly increases the rate of heat loss from the body into the surrounding air. In hot weather, a pig’s respiration rate can climb above 50 breaths per minute, a clear sign of heat stress, and can exceed 100 breaths per minute in severe cases. Despite this effort, respiratory heat loss is less efficient than full-body sweating because the respiratory surface area is relatively small compared to the pig’s total body size. Furthermore, the effectiveness of panting diminishes rapidly in environments with high humidity, as the air is already saturated with water vapor.
Vulnerability to Heat Stress and Management
The limitations of their cooling mechanisms make pigs susceptible to heat stress and hyperthermia. Pigs have a thick layer of subcutaneous fat, or backfat, which acts as an insulator and impedes heat loss from the body core to the skin surface. This combination of poor insulation and limited evaporative cooling means that when ambient temperatures rise above their thermoneutral zone (around 22°C for many adult pigs), they struggle to maintain a stable body temperature.
Symptoms of heat stress include increased respiration rates, elevated core body temperature, and reduced feed intake, since digestion generates additional metabolic heat. To mitigate these risks, management must provide environmental controls.
Environmental Controls
- Ensuring access to shade.
- Utilizing cooling systems such as misters or sprinklers for wet-skin cooling.
- Ensuring proper ventilation to remove hot, moist air.
- Providing chilled or fresh drinking water to aid internal cooling and replace fluids lost through panting.