I decided to spend a long weekend in Scottsdale after a new client who had recently relocated from there reminded me how much fun it can be for sun worshipers. So, I escaped the 100+ degree California heat to the 108-degree summer sizzle that undoubtedly helped Phoenix earn its name.
As I lay by the pool living the good life, I thought about how my client described her horses' irritability in the Arizona heat. For nearly all horses (and all mammals for that matter), high temperature and/or humidity can make strenuous exercise prohibitive, especially if the body is not acclimated and in excellent aerobic condition. In some unfortunate cases, heat illness can cause serious physical consequences or be fatal. Knowing how to identify heat illness, treat it early and, preferably, avoid it completely is key to avoiding catastrophe.
Heat illness actually consists of several stages with the most recognizable being heat exhaustion and heat stroke. They can come on fast - especially if your horse is not acclimated to high heat. Although they are most commonly observed with strenuous exercise, they can also occur in a hot trailer or stall.
Heat exhaustion is characterized by high body temperature (often times greater than 104 F), high heart rates (60 beats per minute or greater) and respiratory rates exceeding 80 breaths per minute. The horse appears to “not be able to catch his breath” and cool down. Interestingly enough, depending on the stage of heat exhaustion, sweating may or may not be occurring.
Why? Because horses with heat exhaustion are inevitably dehydrated and, in extreme cases of dehydration, anhidrosis (the inability to sweat) will occur.
In such cases, the horse is in critical condition since a key mechanism to dissipate body heat is no longer available. Remember: Excess heat energy leaves the body as sweat evaporates from liquid to gas and off of the skin surface. Horses with heat exhaustion are fatigued and are clearly working to just breathe. Other signs will include dry, tacky gums and nasal passages and the inability to decrease rectal temperature despite physiologic efforts.
Heat exhaustion will quickly progress into heat stroke if left untreated. Both are serious, but heat stroke is more likely to result in permanent or fatal consequences.
Horses with heat stroke continue to exhibit the signs associated with heat exhaustion, but also begin to show signs of organ dysfunction (due to electrolyte and water imbalances) and neurologic problems. The most common include an altered mental state (stuporous, obtunded or depressed), walking abnormally (drunk appearing) and in more advanced stages, seizure and death.
For horses that survive, organ failure, laminitis and colic have been commonly reported along with pulmonary edema (fluid in the lungs.) OK, OK - enough of the horror story! How do we treat heat exhaustion to avoid it getting to this stage?
Immediately move the horse to a shady area and place him in front of several fans if possible. Fans fitted with misters are also helpful since the mist cools the air that makes contact with the horse. Removing tack, blankets, fly sheets, masks or any item that is insulating the horse is important.
Now, in addition to all of this- the most rewarding chore! Repeated application of ice cold water on a two to three minute interval is advised to help reduce the core body temperature. Since the dissipating heat will quickly warm the applied water, it is imperative that water be scraped away and reapplied as much as needed until the rectal temperature returns to normal.
If you are unable to effectively rinse the whole body, concentrate on the neck, chest and the area of large blood vessels on the inside of the upper hind legs since these areas are richest in major vessels that run close to the skin surface.
Also, since horses in advanced stages of exhaustion do not sweat, the moisture adds evaporative ability to the skin surface, which more efficiently dissipates body heat. Some people also mix rubbing alcohol in with the water, which lowers the evaporation point to allow for quicker dissipation of heat. No problems here - just keep the alcohol out of cuts and eyes!
Horses should be allowed to drink cool temperature to slightly cold water when being treated for heat exhaustion. Many will not drink. It is imperative that in all cases horses receive IV fluid support as quickly as possible. IV fluids provide blood fluid volume, which assists in delivering oxygen and nutrients to tissues as well as balances electrolytes that have been insensibly lost during the heat exhaustion episode.
Some veterinarians may choose to administer medications that can protect the horse from heat shock, which can occur when cells run out of energy due to lack of proper nutrient and oxygen perfusion. This decision must be made on a case by case basis.
Pay Attention to Heat Index and Provide Access to Water
After reading about this nightmare, you probably figure that the best approach to heat exhaustion is to avoid it altogether. The best way to prevent it is to pay particular attention to the heat index in your area. The ambient temperature only is part of the equation when it comes to heat index. You must also consider the relative humidity.
The heat index is determined by adding the temperature (in degrees Fahrenheit) to the percent humidity. Rule of thumb: If it is below 120, you are riding in safe conditions. Between 120 and 150, things can get a little dicey, especially if the humidity is equal to or greater than the temperature. In these situations, you may only want to do a light ride and consider wetting your horse before you start.
Anything above 150 is an absolute thumbs down! Do not get on and ride if you are facing this type of heat index - there will be other days to ride. If you do find yourself riding in a risky heat index, make sure to provide your horse with plenty of fresh cool water and amble opportunities to cool down and rest in the shade.