This is the first in a series of articles discussing equine related veterinary issues. Each week will focus on a different topic, from advancements in diagnostic imaging to the latest therapies for arthritis.

 

As hot summer days are upon us, it’s a good time to stop and think about how to prevent subjecting your horse to overheating, or worse, to heat stroke. Being able to predict when your horse is at risk is key to being able to train, compete or just trail ride in the summer months.

In horses, as in humans, temperature is controlled by a specific part of the brain called the hypothalamus. This organ is responsible for coordinating all responses to excess heat including sweating, vasodilatation and flaring of the nostrils.

The hypothalamus also signals the body to decrease its basal metabolism to produce less heat, especially when ambient temperature and humidity rise. It is through these mechanisms that the core temperature is tightly regulated (99 degrees – 101 degrees).

Much like a human athlete, a horse will lose most of its heat through sweating (70 percent) and evaporation. As much as 15 liters of sweat can be lost every hour during intense exercise and this sweat is made up of water and electrolytes.

 

Prediction

A Heat Index formula is provided by the National Weather Service and can be found at www.crh.noaa.gov and provides an equation for plugging in ambient temperature and humidity (www.usairnet.com) to determine heat index.

Caution is advised if exercising your horse at heat index temperatures greater than 90 degrees, and it is dangerous to exercise at over 105 degrees.

Another simple and useful way to evaluate the relative heat is to add the temperature and humidity together. If the total number is less than 120, then moderate exercise should be safe. Values above 150, particularly if humidity contributes to more than half of this number, causes your horse’s natural cooling mechanisms to be compromised.

Values greater than 180 are unsafe to horse and rider ,and equestrian competitions may need to be delayed or cancelled pending cooler, less humid weather conditions.

 

Prevention

Preventing susceptibility to heat stress should start long before summer. Keeping your horse fit and not overweight and on a low grain diet, allows less body heat production and more efficient heat loss through sweating and evaporation. Heat removal is more difficult in overweight or heavily muscled breeds compared to lighter muscled horses.

Preventing dehydration is important in avoiding overheating because sweating and evaporation is the primary mechanism for cooling in the horse. Providing clear, cool drinking water at all times and adding electrolytes into the feed is an important way to support your horse’s cooling system.

Also, having air coolers or large fans with or without water misters goes a long way toward preventing overheating in stalled horses or horses getting ready to compete.

Locating your horse in the shade and in a breeze is also a very effective way to protect your horse from overheating even on a very hot and humid day.

 

Symptoms

It is still possible, despite your best prevention efforts, for a horse to get overheated or heat stroke, so it is important to be able to recognize the warning signs early.

These signs include a refusal to work; hot, dry skin; and decreased sweating and increased respiration rate. The rectal temperature can be elevated into the range of 102 degrees – 106 degrees.

Capillary refill times can be elevated and should be tested. In a normal horse, when you apply pressure to the gum line with your thumb and then release it, the pink color should return within two seconds. If it doesn’t, your horse is not fully hydrated and may need to be hydrated either orally or intravenously.

Another important sign of dehydration and potential overheating is loss of skin elasticity. The skin elasticity can be tested by pinching the skin on the side of your horse’s neck. If the skin tents and does not immediately snap back, then your horse is showing another sign of dehydration. An elevated heart rate and respiration rate also may indicate heat problems.

 

Treatment

Consult your veterinarian if overheating or heat stroke has occurred. Immediate steps should be taken to treat it. Move your horse to a cool area with a breeze, if possible. If there is not a good breeze, then a large fan will assist cooling by increasing evaporation.

Offer your horse small sips of water, but do not allow your horse to drink too much immediately as this can induce a bout of colic.

Begin cold hose therapy or use a large sponge to apply cold water over the great veins and arteries of the neck and of the legs. Cooling the blood in this fashion acts like a radiator.

If symptoms don’t subside rapidly, your veterinarian may initiate further treatments such as cold IV fluids and cold enemas to reduce body temperature back to normal.

 

Dr. Alexander Daniel is a member of the Royal College of Veterinary Surgeons and a staff veterinarian at the Alamo Pintado Equine Clinic.