Is my horse too hot?

The normal rectal temperature of an adult horse is 37C-38.5C (99-101.5F), that of newborn foals tends to be a little higher at 37.5C-39C (99.5-102.2F) while that of donkeys is 36.5C-37.8C (97.2-100F). Rectal temperature is a useful parameter to measure when assessing your horse’s health. If you are unsure of how to take the temperature, be sure to ask your vet who will be able to advise you. Most people tend to use a standard digital thermometer available from any chemist shop.

What does an increased temperature mean?

When considering the cause of an increased rectal temperature, history is very important. If the horse has been exercising during high environmental temperatures, heat stroke is more likely. Whereas if they have a history of exposure to others with an infectious disease, then pyrexia due to a bacterial or viral cause may be more likely. However, a clinical examination by a vet may be necessary to determine the cause and to provide appropriate treatment. 

In general, we can categorise a higher temperature as either pyrexia or hyperthermia. In the case of pyrexia, the body’s internal mechanism for regulating core temperature is reset to a higher level, usually in response to inflammation or infection. And in hyperthermia, the body’s ability to cope with excessive heat is overwhelmed, either due to excessive heat production or exposure, or both, and the body overheats. It is important to differentiate as treatment of these conditions is different. Antipyretic drugs for example, will not help in cases of heat stroke. 

Pyrexia:

The list of possible causes of pyrexia is a lengthy one. It can be broken down into infectious or non-infectious causes. Your vet will need to ask you about your horse’s recent history as well as that of any horses yours has been in contact with, to start to narrow down this list to the most likely causes.

Some common infectious diseases include, Streptococcus equi equi (strangles), Equine influenza, Equine Herpes 1 or 4. Non-infectious causes include, peritonitis, pneumonia, colitis, endocarditis, or less commonly, neoplasia such as lymphoma. Immune mediated diseases can cause pyrexia but are quite rare. 

Your vet will need to carry out a full clinical exam to look at every body system that may be affected. This may include blood samples to determine the white cell count; as well as to assess the overall state of health. Other