Why a Pig’s Mud Bath Works
A pig’s problem is not that it never gets warm; it is that it has little capacity to cool itself by sweating. Sweat cools many mammals when it evaporates from the skin, carrying heat away. Pigs have very few functional sweat glands, so they rely more heavily on behavior and their surroundings to shed excess heat.
Evaporation Does the Cooling
Mud helps partly because it holds water against the skin. As that water evaporates, it takes heat with it. The cooling effect depends on evaporation: in damp, humid conditions, water evaporates more slowly, so a mud coating may be less effective than it is in hot, dry air. Pigs may also seek shade or water, but a wallow gives them a way to cool much of their body at once.
A Coating With Other Uses
The dried layer can provide a barrier between skin and sunlight, and it can make it harder for biting insects to reach the skin. That protection is useful because pigs have relatively sparse hair and exposed skin can be vulnerable to sun and pests. The mud does not work like a powered air conditioner; its cooling comes from water changing into vapor, while its coverage offers a physical shield.
A wallow therefore solves several problems with one behavior: water in the mud can carry heat away as it evaporates, and the coating left behind helps shield the pig from sun and insects.
