INTER-BREED VARIATION IN THE HORSE WITH REGARD TO COLD ADAPTATION - AREVIEW

The scientific literature on adaptation to cold in the horse is scant. Yet, if one considers the geographical range of horse rearing around the world one can see that much of it lies in cold-climate zones or th ose with a cold winter. An examination of the literature on thermoregu lation in mammals brings out a number of questions relevant to horse b reeds. The answers to some of these questions may be of practical valu e in horse husbandry. An animal adapts to cold first and foremost by r educing thermolysis, and also by increasing thermogenesis. These are a chieved through a variety of mechanisms, examined in this paper both i n the individual animal and at the level of the population to which th e individual belongs. Seasonal reproduction, for example, can be inter preted as a form of cold adaptation. The mechanisms involved often com bine resistance to cold with resistance to food shortage, and body res erves play an important part. Aerobic metabolism, in which fatty acids are broken down, tends to take precedence over anaerobic metabolism, in which glycogen is broken down. The former is suited to prolonged, l ow-intensity effort, while the latter is suited to intense exertion of short duration. By examining all these phenomena one can work out the archetypes of the horse adapted to cold conditions and, conversely, t hose adapted to heat. These prove to match up quite well with the trad itional classification into cold blood and warm blood. Most breeds can be placed somewhere between the two extremes. However, it is worth no ting that the various breeds of trotters found in the cold climatic co untries are the most northerly form of warm-blooded horses. Improving environmental conditions would therefore seem to have some economic li mits.