By Annie King, DVM, Equine Ambulatory Department, Pilchuck Veterinary Hospital               

With summer finally here and competition season in full swing, it is important to remember that high temperatures encountered during the summer months can have serious effects on our equine companions. Whether your horse is a beloved pasture-pet or competing at the highest levels, there are things you can do to help him or her handle the increase in temperature.

First and foremost, always provide your horse plenty of fresh, clean water. Horses that normally drink 5 to 10 gallons of water a day in cool weather may need to drink 20+ gallons of water a day to meet their maintenance requirements and replace losses in sweat during periods of hot weather. A sweating horse can produce as much as 6 to 15 liters of sweat in one hour1! Not only does this result in losses of body water, but also in losses of the important electrolytes sodium, potassium and chloride. For this reason, all horses should have access to a salt block. Horses that are in regular work during hot weather may require additional salt or electrolyte supplementation.

Horses in any level of work may need adjustments made to their schedules during hot weather. This can be achieved by decreasing the length or intensity of an individual workout and taking frequent rest breaks. Another option is to ride early in the morning when temperatures are at their lowest. As always, take the time to warm up and cool down your horse before and after a workout. Extended cool-down times are essential in high temperatures when the horse’s natural cooling mechanisms have been affected. Help your horses dissipate heat more rapidly during cool-down by moving them to a shady area, allowing them to drink, and hosing them with cool water.

Conditioning is essential to the level of work your horse is able to tolerate in hot weather. Conditioning improves the cardiovascular, respiratory and muscular systems, making horses more efficient at coping with the additional stress of increased heat during exercise. Tailor your horse’s conditioning program to achieve the intended level of exercise by working slowly and consistently. For some horses, even a 20-minute walk in hot weather can be a tough workout!

So, is it ever too hot to ride your horse? While it is probably a rare occurrence here in the Northwest, there are times when the heat and humidity will make it necessary for you to adjust your horse’s exercise routine drastically or possibly suspend it completely.

Luckily, there is an easy formula that can help you decide if a decrease in exercise is appropriate for your horse on a given day: Simply add the outside temperature to the relative humidity2. If the sum of these numbers is less than 130 (e.g., 80°F with 40% humidity), most horses can regulate their temperature appropriately. If the sum lies between 130 and 180, your horse’s cooling systems will be challenged and adjustments will need to be instituted. If the sum exceeds 180 (e.g., 95°F with 90% humidity), the cooling system of even the most well-conditioned horse is severely compromised.

Other factors influencing the appropriate amount of exercise include body condition and age. Very young horses and those that are very muscular or fat are less tolerant of high heat and humidity and therefore require additional concessions when exercised in hot weather.

1. “Horses Exercising in the Heat - Thermoregulatory Demands and Strategies for Mitigation of Exercise-Heat Stress”. R.J. Geor. 9th Congress on Equine Medicine & Surgery in Geneva, Chuit P. and Montavon S. (Eds.) Ithaca: International Veterinary Information Service (, 2005; P1925.1205.

2. “Heat stroke”. Steven M. Haugen, DVM. First Aid / Emergency Care: American Association of Equine Practitioners website (; Sep 24th, 2003.

Born and raised in North Carolina, where she started riding horses at the age of 6, Dr. Annie King is a member of Pilchuck Veterinary Hospital’s equine ambulatory department. More information on PVH’s comprehensive equine services can be found at, or join PVH on Facebook at