Kept in stables or/and blanketed, horses lack stimuli (temperature fluctuations) triggering the activity of thermoregulatory mechanisms. They don’t need to exercise hair erector muscles, nor to dilate or constrict arteries, nor to activate the sweat glands, nor to prepare or deplete healthy fat reserves. All muscles atrophy without exercising for a period of time. If an animal in this state is suddenly exposed to the cold, they will not be able to activate necessary thermoregulatory mechanisms. As a result the internal body temperature could drop too low, that would lead to disruptions in metabolic processes. This can affect, for example, the production and migration rate of white blood cells and antibodies, with partial disabling of them. The result is a stressed animal with a disease or infection hosting internal environment. The germ is nothing, the terrain is all (Louis Pasteur). Consequentially germs or viruses in the body get a perfect opportunity to over breed.

 Besides the fact that the natural thermoregulatory mechanisms can only be fully utilized when a horse is kept in their species-appropriate living conditions, there is an anxiety and stress factor that horses inevitably experience when cut off from their basic needs and kept in ways unnatural for this species (stabling, separating from equine companions, forced exercising, lack of continuous fiber uptake, etc.). This stress also makes them less capable of coping with cold.