Aug 16, 2020

The Weather is Heating Up; Keep Your Horse's Temperature Down

A horse being cooled off in the vet box. USEA/Leslie Mintz Photo.

This article was originally published on the USEA website on June 21, 2017.

Leading equine researcher and scientist Dr. David Marlin has been studying thermoregulation and cooling of horses for over 20 years. Marlin shares his advice to keep you and your horse safe if you are training and competing in warm or hot weather.


If the weather suddenly becomes warmer, don’t attempt to try to acclimatize your horse by exercising it in the hottest parts of the day if you are competing within a few days. When warm/hot weather appears suddenly, no horses will be acclimatized to training/competing in the heat. Acclimatization takes two to three weeks of regularly exercising in the heat. If you start now your horse is likely to be worse by the weekend as in the first three to five days horses’ ability to deal with heat and exercise gets worse before they start to improve and competing could be a major health risk.


If you are traveling with your horse in warm weather, leave very early or as late as possible, preferably after sunset. It’s not only that it's cooler, but the chance of hitting traffic is less. The worst thing for a horse is to be standing in a trailer that is stationary on hot roads at temperatures that may reach the high 80s or 90s – unless, of course, you have air conditioning. Horses may lose six to eleven pounds per hour in warm weather and so could be considerably dehydrated after a four- to five-hour journey in the hotter parts of the day.


You must accept that your horse will not be able to do the same amount of exercise in the heat as it would in cooler weather. Your horse will produce more adrenaline in hot weather and use up muscle energy stores (glycogen) more quickly. Dehydration also increases adrenaline which compounds the problem. Therefore, if you compete just as hard as you would in cooler weather your horse will tire earlier. If you don’t compete as hard your speed will be slower but your horse will be at a lower risk of heat-related illness.


Your horse must have clean water at all times. Your horse may drink considerably more in hot weather. If you use buckets you should consider putting another bucket in the stable. Allow your horse water right up until the time you are going to take him to compete. You can also allow him to drink after warming up and before competing. He will have a very strong urge to drink immediately after exercise and you should allow him to do so. There are many myths about water and exercise. Cold water does not cause problems. Large volumes of water do distend the stomach, but that is also the mechanism by which the stomach knows to empty and allow the water through into the small intestine.


If you have not been feeding electrolytes on a regular basis then do not try to suddenly load in large amounts (e.g. 100-200 grams). It will not replace any bodily deficits and it may cause feed refusal or gastrointestinal upset. If you have not been feeding electrolytes regularly then start by feeding 50 grams of a balanced electrolyte split between at least two feeds. Do not be tempted to try and load the day before or the day of competition. If you are providing electrolytes at or during an event, before or after competing or between rounds or phases, then you can provide electrolytes in feed or in pastes or in water. If you provide electrolytes in water then your horses should have the option to drink plain water as well. You can offer the electrolyte water first and if this is refused offer then plain water. There is no difference in the speed of uptake between electrolytes in water or dry electrolytes given in feed. If you provide electrolytes in water then aim for a ratio of around 5-6 grams of electrolyte for every liter of water. In studies the acceptance decreases as the ratio increases above this (i.e. more horses will refuse if given water with 9-10 grams electrolyte per liter of water).


Horses need less time for soft tissues (muscle, tendon, ligament, etc.) to “warm up” in hot weather. You should aim to reduce the time you spend warming up by around 50 percent. After warming up, you should try to find shade to stand in and you can cool your horse with water and ice (if available). Reducing your horse's body temperature does not counteract the other physiological effects of warming up. There is also no reason why you cannot go into competition with a horse that has been “wetted”. Covering the horse with water means that the horse evaporates this rather than has to use his own sweat.


The most effective way to cool a horse is with cold water all over the body surface, especially in front of and behind the saddle if you are riding and being given water containers to pour on or all over if you are not riding and the tack is removed. The water really needs to be 60 degrees Fahrenheit or less. Warm water is not any good for cooling down horses except by evaporation and this is much less efficient when horses are not exercising. If ice is available, then use it to cool down the water. Water that is around 40 degrees Fahrenheit is ideal and very effective at cooling. It does not cause constriction of blood vessels and prevent the horse cooling down – this is a myth. You should not concentrate on large veins or arteries or large muscle groups (another myth) and, in fact, this will be much less effective. You do not need to scrape off water – another myth! If it sits there, it will evaporate and contribute to cooling the horse. It doesn’t matter how you get it on – buckets and hoses best; sponges ok. Cold water does not cause muscle cramps or tying-up.

This is the only study I am aware of that shows NOT SCRAPING does NOT cause skin temperature to rise! Blue blocks show period of iced-water application. Periods in between represent no water application and NO SCRAPING. Skin temperature and all other body temperatures still fall even though there is NO SCRAPING! (Cooling evj, 1998.)

Blankets and Clothing

If you do put on a sheet then make sure it’s a white one. White material reflects some heat whilst dark colors absorb radiant heat. The same goes for your own clothing. If possible, ride in white and wear a white helmet.

Heat Stroke / Heat Exhaustion

Signs that your horse may be suffering from the heat include:

  • Lethargy
  • Panting (faster shallow breathing)
  • Nostril flaring
  • Increased rectal temperature
  • Decreased appetite and thirst
  • Dark urine
  • Reduced urination
  • Reduced performance
  • Dark mucous membranes
  • Muscle spasms
  • “Thumps” (synchronous diaphragmatic flutter)
  • Abnormal (irregular) heart rhythm
  • Slow recovery after exercise

This is often referred to as heat exhaustion, but if not managed properly and quickly can progress to heat stroke. This may include ataxia (being unsteady on the feet) and/or collapse.

If your horse does go down then continue to cool it aggressively and send for a vet! If you are concerned that your horse may have severe heat stroke then it’s important that you seek veterinary advice as soon as possible.

Severe heat stroke/heat exhaustion can lead to renal failure, myopathy (muscle damage), laminitis, liver failure, and can be fatal if not treated promptly. If you think your horse may be suffering heat-related illness, move your horse into the shade and start to cool by pouring large amounts of water all over the body. If ice is available then use that to cool the water. Do not worry about scraping the water off, just apply more water. If your horse has developed heat exhaustion/heat stroke you may need to cool continuously for 10-15 minutes before you start to see an effect. You are extremely unlikely to do any harm and your horse is at much greater risk from not being cooled. If shade is available nearby and the horse is steady on its feet then move into the shade whilst continuing to cool.

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