Hot Weather Considerations

Dr. Jennifer Wright 

It’s HOT HOT HOT outside, and it would appear that the humid summer weather is here to stay! Horses (and riders) are at great risk of experiencing heat stroke, dehydration or other debilitating problems associated with heat in this type of weather, as their primary method of cooling (sweating and evaporation) is compromised. How do you know if you may be potentially placing yourself or your horse at risk by riding? A good rule of thumb when assessing how the heat will affect your workout is to measure the Heat Stress Index (HSI). The HSI is determined by adding the ambient temperature (degrees Fahrenheit) plus the % humidity (temp + humidity = HSI).

  • HSI less than 120 = normal riding should be no problem
  • HSI 120 – 150 = lower the intensity of the workout, shorten the workout OR ride early in the morning or late at night
  • HSI 150 – 180 = lower the intensity of the workout, shorten the workout AND ride early in the morning or late at night
  • HSI 180 or greater = no forced exercise for your horse, and be sure that your horse has plenty of shade and drinking water
Hot Horse

Hot Horse












Of course we understand that there will be times (i.e. competition) that your horse must work hard in warm, humid weather.  Things that you can do to help prevent your horse from experiencing a dangerous body temperature rise after a strenuous exertion:

  • Pre-cool your horse by cold hosing or sponging their entire body, do NOT scrape off the excess water, then tack up. The wet coat saves your horse from having to sweat to commence the cooling process.
  • After working, un-tack immediately and cold hose or sponge their entire body. It is very important to scrape the excess water off at this time so it does not act like an insulating ‘blanket.’  Walk your horse in the shade to establish air flow and aid evaporative cooling.

If your horse appears stressed, apply very cold water or ice packs to the large vessels along the inside of their hind legs, belly and jugular veins. Continuously scrape the water off and reapply.


Prevent Heat Stroke

Prevent Heat Stroke










Consider the concept of the “6 Minute Threshold” when working your horse in warm, humid weather.  Combinations of high heat and humidity severely impact sweating and evaporation, your horse’s main cooling mechanism.  Horses are able to sustain strenuous activity in conditions with a high HSI for 6 to 6 1/2 minutes before experiencing a dangerous body temperature hike and being at risk for fatal heat stroke.  For some performance disciplines, the 6 Minute Threshold is very important to remember…for example, a dressage horse works strenuously both during the warm up and the test, whereas it typically takes a show jumper less than 6 minutes to complete their course.Before you ride, make sure that you know how to recognize the dangerous signs of heat stroke in your horse.  Signs may include:

  • Profound lethargy, distress or agitation (i.e. violently kicking out)
  • Persistently elevated rectal temperature, heart rate and respiratory rate at rest
  • Cardiac irregularities or “Thumps” (looks like hiccups, but is associated with electrolyte imbalance and dehydration)
  • Marked dehydration with lack of thirst (prolonged skin tent over cheek muscle)
  • Anhydrosis (not sweating)
  • Muscle cramping or rhabdomyolysis (tying up)
  • Weakness, ataxia, or collapse

If any of these signs are noted in your horse, stop work immediately, move them to the shade, cold hose or sponge their entire body continuously, apply gel ice packs to the large blood vessels along the belly and legs, offer frequent sips of cool water and call your veterinarian.  Happy riding and be safe!


Prevent Heat Stroke

Prevent Heat Stroke