Hot Topic: Heat Stress and Horses

Sunny summer days exert a certain power over horse owners, urging us to get out and ride NOW, before winter slaps us senseless again. However, summer temperatures can put your horse at risk for heat stress – a common condition that can have serious consequences if not recognized and treated early enough.

On those really hot summer days, horses appreciate
having plenty of fresh, cool water -- inside and out!

CAUSE AND PREVENTION

Horses have a large body mass relative to their surface area, which makes them good at staying warm when it is cold, but not as efficient at cooling off when it gets hot out. For this reason, your horse’s “perfect day” might feel slightly chilly to you. Says Jennifer Jackson, DVM, of the Kamloops Large Animal Veterinary Clinic in Kamloops, BC, “Horses are most comfortable at 50-60 F, and concerns should be in motion once the temperature gets to 75 F or higher. Humidity also plays a part, because it affects the ability of the horse to cool itself through sweating.”

Still, if your horse is just standing around in the shade, with access to plenty of water and a source of salt, he’s not likely to have a problem. The trouble most often occurs when we work the horse, as working muscle generates a tremendous amount of internal heat. In fact, more than 50% of the energy a horse uses to move around converts to heat. Hotter muscles require more oxygen to make use of energy, and at a certain point, the body’s ability to take in oxygen can be outstripped by the demands of the muscles, leading to heat stress, also known as heat exhaustion. Long periods of exercise or short but intense periods of exertion are most likely to be problematic.

The horse’s body attempts to prevent heat stress mainly through the mechanism of sweating, which dissipates heat from the skin when the moisture produced evaporates. However, when temperatures are high, the horse may not be able to sweat enough to remove the necessary amount of heat. Humidity makes this scenario worse, as it slows down the process of evaporation.

The body of the horse also tries to dissipate some excess heat through rapid breathing, which can lower the heat load by about 15% if each breath coming in is cooler than the air being exhaled. Of course, the higher the ambient temperature, the less difference there will be between the inhaled and exhaled air, making this process less efficient.

Lack of fitness will also make the horse less efficient at getting rid of excess heat, and much more vulnerable to heat stress. A fitter horse has better circulation, and good circulation is necessary to help move heat from the muscles to the skin and lungs, where it can leave the body. A fit horse also utilizes oxygen better than an unfit horse, giving him a larger “buffer zone” before his muscles experience heat exhaustion.

For this reason, Dr. Jackson emphasizes conditioning as a critical element in the prevention of heat stress. “When it’s hot out,” she says, “it is even more important than usual to make sure your horse is fit enough to perform the task at hand.” However, there are more pieces of the puzzle that horse owners should be aware of. “Also make sure your horse is hydrated before beginning exercise,” says Dr. Jackson, “as dehydration will play a part in a horses ability to cool itself because it affects the sweat response.  A horse should be kept hydrated and have adequate salt intake (availability).  Electrolyte imbalances could additionally play a part in heat exhaustion, so you may want to think about adding electrolytes to your horse’s feed or water. Lastly, use common sense when conditioning and performing with your horse, and pay attention to his body language.”

If a horse is experiencing heat stress, your ability to recognize the symptoms can help prevent the problem from getting out of hand.  In terms of what you might see, Dr. Jackson states, “The heat stressed horse may sweat profusely or not at all.  They may tremble and seem ataxic(wobbly on their feet).  Respirations may be shallow and fast and heart rate will jump. They may not act thirsty, even if they are severely dehydrated.” Left untreated, a horse suffering from heat stress may begin to seizure and could sustain serious damage to the brain, heart, other muscles, and kidneys.

If you suspect your horse is suffering heat stress, time is of the essence. Says Dr. Jackson, “A heat stressed animal needs to be cooled down immediately. This can be done by applying cool water to the animal’s body. Exercise should be stopped immediately and the horse should be moved out of the sun but to a place where there is good air flow.  Call your vet.”

HYDRATION

 Making sure your horse stays adequately hydrated is another important aspect of preventing heat stress and other related issues. Most horses will naturally consume more water when it is hot and they’ve been sweating, but nonetheless, dehydration can happen, and it has potentially dire consequences. Explains Dr. Jackson, “Dehydration may start out as a minor problem on its own, but soon gets serious because a magnifying effect can happen.  Health problems that are normally of minor consequence will become amplified in a dehydrated animal.  Without proper hydration, many of the regulatory processes of the body become impaired, and the more severe dehydration becomes, the less likely the animal will recover without veterinary assistance.  In general, early intervention leads to better outcomes.” Dehydration can lead to muscle cramping, heart problems, metabolic disturbances and colic.

It is therefore critical to make absolutely sure our horses have an adequate water supply during hot weather spells. Keep a close eye on buckets or small troughs which may have to be replenished more frequently than usual, and make sure that automatic waterers are working on a continual basis. Even streams can dry up in certain locations during hot weather, so if you are relying on a variable natural water source, it should be monitored as well. Lastly, be sure sources of water are free of offputting contaminants: a dead bird or rodent in a water tank can cause horses to refuse to drink, even if they are desperately thirsty.

Traveling to new locations with your horse, as many of us do for shows or camping in the summer, can also put your horse at risk for dehydration. Many horses will refuse to drink during trailering or at rest stops, even if they have been sweating profusely due to heat or nerves in the trailer. To deal with this issue, trick trainer Theresa Madok of Alturas, CA, suggests teaching your horse to drink on cue. “I teach all my horses to drink on cue,” says Madok, “as this can really be a life saver. I do this by taking them to water when I know they are thirsty (such as after a training session), giving them a verbal cue such as ‘drink’, allowing them to drink, then rewarding them with a treat after they’re done. You would be surprised at how quickly most horses catch on. I can then get them to take a good long drink just before they get into a trailer, and usually again at rest stops.”

Another travel-related issue is that many horses may be hesitant to drink water in a new location if it tastes or smells different from the water they normally drink.  To avoid this situation, it can be helpful to get your horse used to drinking flavored water, both with and without electrolytes (see below for more on electrolytes).  The familiar flavoring can then be added to a bucket of water at the new grounds to help encourage your horse to start drinking the “funny tasting water”.

As for what to do with a hot horse post exercise, it is best to ignore the old myth that a hot horse should not be allowed to drink until it has cooled down. Unless the horse has been galloping very hard or for a prolonged period of time, drinking right after exercise will not harm them. In fact, recent research has shown that withholding water after exercise may be potentially harmful because it prolongs dehydration. Horses are more likely to drink soon after exercise when their thirst drive is high, and they need that water intake to replace fluids lost to sweating. While it is still inadvisable to allow a very hot horse to drink ice cold water after extreme exertion, it is a good idea to allow the horse to drink in most typical scenarios.

ELECTROLYTES

 

Closely related to the problem of dehydration is the issue of electolyte imbalance. Electrolytes are substances that become ions in solution and are then able to conduct electricity. The balance of the electrolytes in living bodies is necessary for the normal functioning of cells and organs. Sodium, chloride and potassium are electrolytes lost when horses sweat. This depletion of electrolytes can trigger serious health issues such as colic and Exertional Rhabdomyolysis (ER), also known as “tying up” .

Most horses that have a healthy diet and free access to salt (sodium chloride) do not need additional electrolyte supplementation. However, horses involved in demanding sports like racing, endurance riding or eventing may benefit from the administration of additional electrolytes. There are a number of electrolyte products formulated especially for horses. In general, you should not give electrolytes made for cattle or other livestock, or electrolytes with a high amount of sugar to horses. Consult with your veterinarian if you think your horse may need electrolyte supplementation beyond salt.

Salt itself should be available to horses at all times, but is of critical importance in the summer, as the regular consumption of salt helps prevent dehydration in horses by triggering the thirst response. Horses lose a great deal of salt in their sweat (far more than humans do on a proportional basis), and it is believed that this may be why horses that have been sweating profusely do not always show an inclination to drink, even though they are dehydrated. When humans sweat, we lose proportionally more water than sodium, so our blood concentration of sodium increases, triggering the thirst response. Horses, however, lose so much sodium in their sweat that their blood concentration of sodium actually decreases if their salt intake is not adequate to compensate for the loss.

Fortunately, horses naturally choose to consume salt, usually in just the amount they need.  While many people choose to provide their horses with salt in block form, some experts feel that loose salt is better for horses as it is easier for them to consume than blocks, which were designed with the rough, abrasive tongues of cattle in mind. Either way, an average sized horse in light to moderate work generally needs to consume 1-2 oz. of salt per day, depending on the amount they are sweating. If you do use blocks, it is a good idea to weigh a new block before you give it to the horse, then weigh it again every few days to see if it is being consumed at an adequate rate. If not, try switching to loose salt. If you have a horse that doesn’t consume enough salt or doesn’t drink enough water, adding up to 1 oz. of loose salt to a mash each day can stimulate drinking.

As for what type of salt is best – iodized (pink/red), plain (white/grey), cobalt (blue) or a mix of minerals added (often brick colored), this depends on what minerals are excessive or deficient in your horse’s diet.  Your veterinarian or local agricultural cooperative can likely tell you what minerals typically need to be added in your region.  Keep in mind that if you are adding any other mineral supplements, you may not want to add additional minerals in the salt. It is also best to avoid flavored or sugared salt blocks, as this can encourage excessive consumption. 

           As with most problems, prevention is better than cure, so keep the reality of heat stress in mind when that siren sun starts calling you to jump on your horse and ride. Just remember that if it feels hot to you, it feels even hotter to your horse, so perhaps skip the ride and spend some time bonding in the shade.