Ways of keeping warm
A horse's body temperature is 37-38 degrees Celsius and their body will react in a way to maintain this temperature in the body and keep levels constant. The body temperature is important for the normal running of the body systems and changes may lead to problems. The most active organs produce the most heat, this includes the muscles, the liver and the digestive system. Receptors called thermoreceptors monitor the temperature of the horse, if they detect that the temperature is falling they will send messages to other areas of the body in order to do something to warm up the horse.
- If a horse is cold then the hairs in their coat may stand on end, this is called piloerection. When the hairs stand up it traps a layer of air in the coat which helps as an extra layer of insulation. These hairs lye flat if the horse then gets too hot to let the heat quickly escape. The use of a rug on the horse will flatten down the hairs and prevent this from happening.
- Vasoconstriction may also happen, this is when the blood vessels constrict and reduce the amount of blood going to the surface of the horse's body. Due to this, less heat will be lost from the blood into the surrounding cold air.
- The shape of a horse also helps to keep them warm. They have a large surface area to volume ratio meaning that for the amount of heat that is kept in the inside, less will be lost through the surface of their skin. Their legs also have a very low blood supply (which is why injuries here take longer to heal). This means that not much heat is lost from the blood flowing through these areas.
- Counter-current heat exchange also happens. This is when the blood that is on it's way back to the heart and lungs after being near the horse's skin is warmed before it gets there. This is due to it passing near by to the blood in arteries and the heat is transferred from one to the other.
- Circulation shunts also happen in the feet of the horse to prevent them from becoming too cold. This is why your horse's feet don't freeze! This isn't well understood but it is thought that blood is moved to these areas to warm them up.
- The horses metabolism may also increase which would result in more heat being produced.
- Horses may also shiver if they get cold, this extra movement of muscles will help to produce heat and warm them up.
- Horses also develop a thicker coat in the winter, this adds to the amount of insulation they have compared to the summer.