In nature, the environmental temperature is constantly fluctuating. The horse has about six different ways to maintain its body temperature of 38 degrees even though it is exposed to the changing weather, such as sun, wind and storms.
1. Skin - Works as an insulating layer
2. Coat - Changes twice a year to adapt to different seasonal temperatures
3. Arteries - Can enlarge and constrict when necessary
4. Sweat Glands - Can cool through evaporation
5. Shivering and Movement - Creates heat
6. Hairs Raise and Lower – To fluctuate temperature when needed
If the horse is stabled or covered these natural thermoregulatory mechanisms cannot function optimally, which can lead to colds and sickness.
Over the last few millennium the wild horse has spread over the entire world, partially due to humans and partially due to its own movement. No matter where the horse has been, the air temperature has continued to fluctuate during the day and night as well as having a seasonal rhythm; sometimes very little and sometimes greatly.
For a mammal to survive, its internal body temperature must be kept at a particular range. If the horse's temperature exceeds or falls below this limit the chemical reaction at cell level can cease to function or does not function properly, this is when health problems can start.
So, no matter where the horse lives, either in a hot climate or an extremely cold climate, it does not seek excessive shelter. The horse's skin has a connection to the environment through its sensory organs, which gives the organism information about the outside world. The skin is also able to excrete metabolic waste products such as proteins (in the form of hair or horn salts, fluids etc).