How hot is too hot to ride?
It’s going to be a hot weekend. How hot is too hot to ride? Many of us have seen those horse heat index charts or number ranges posted on social media every summer. They all list the added value of the humidity index plus the temperature in Fahrenheit added together to tell you whether or not it is too hot to ride. But what about those of us outside the USA who use Celsius to measure temperature? Each heat index I have seen varies and calculates out to a different value in Celsius. So, which one is right? With some research and a little math, I have developed a Celsius-based specific heat index for horses.
First, a few caveats. Since I found multiple heat indexes aimed at horses that varied quite a bit in their recommendations, the graph I developed is a modified version of all of them. I also couldn’t find much for research into how these indexes were figured out for horses. They seem to be primarily based off human heat indexes. Basing them off human indexes isn’t a bad thing, after all, we are also working hard in the same temperatures and don’t want to risk heat stroke ourselves. What would happen to our horse if we pass out from heat stress while riding? Equestrian heat safety really requires considering two species.
While veterinarians and researchers all recognize the risks and dangers of heat stroke and heat exhaustion as well as dehydration in hot temperatures, there is very little research into the exact ranges. Heat stroke is serious, tissue damage and tissue death can begin to occur when internal body temperatures reach 40.5°C! The body can shut down and organ damage can result which can quickly lead to death. Heat stroke is an emergency and requires immediate veterinary care. For more information on heat stroke and heat exhaustion in horses check out these links (otherwise this post will get too long) https://aaep.org/horsehealth/heat-stroke, https://aaep.org/horsehealth/keeping-horses-cool, https://aaep.org/issue/summers-coming-hot-weather-care-horses.
I am a subscriber of the “better safe than sorry” school of thought, so I stuck closer the lower index values when adapting the charts. It is also worth considering the geographic climate you are located in and the temperatures your horse is used to. Here in Canada, we get heat warnings for the low 30°C range, whereas that’s a comfortable day in Australia during the summer. There really is no comparing the heat tolerance of a horse in Canada or the UK to a horse in Texas or Australia. Your veterinarian can help give you better direction for your geographic location.
How do you use this chart? It is all colour coordinated for your convenience. Green is good to go ride and have a great time in anything below 70 when you add the humidity and temperature in Celsius together. The yellow (70-89 heat index) range means use some caution when exercising and cooling out your horse. Most horses can naturally keep cool by sweating, but old horses, young horses, obese horses and some horses with health conditions (like insulin resistance/equine metabolic syndrome or Cushing’s) or horses that cannot sweat may find it harder to regulate their body temperatures and cool off after hard work so they may benefit from using cool water to help them bring their temperature down. Make sure your horse drinks water after work, and make sure you do too.
The orange range (90-109) means use extreme caution, your horse’s ability to naturally cool themselves and regulate their temperature is reduced during this range, which increases the risk of heat stress. Use plenty of cold water to help your horse cool off after exercise. It is a good idea to keep work light or wait to ride at a cooler time of day. Old, young, sick, and obese horses may have an even harder time regulating their temperature and are at higher risk of heat stress and heat stroke. Give your horse a good drink of cool water as some horses won’t drink cold water.
The red range (110-124) means danger, your horse cannot regulate their body temperature by sweating alone. Worked horses can develop heat stroke which can result in death. You need to use ice as well as LOTS of cold running water to help bring your horse’s temperature down after work. You as a rider are also at a higher risk of heat stress, so you are better off waiting for a cooler time of day like earlier in the morning or later in the evening to ride. It may be safer to take the day off and not ride, especially if your horse is at higher risk because of their age or health situation. Heat stroke is serious, requires rapid veterinary intervention and can quickly turn deadly. Again, make sure you all drink a good amount of cool water throughout the day and especially after riding.
Finally, the dark red indicates extreme danger above a heat index of 125. Do not ride in these conditions for both horse and human safety. Make sure your equine friend is drinking plenty of water. You can always pick a cooler time of day or just take the day off if you have to. It is not worth the risk of heat stroke, tissue damage, organ damage and death (for both you and your horse) to ride in these conditions. If you are ever not sure, check with your vet. When in doubt, wait the heat out!
Stay safe, remember to drink plenty of water, stay cool and enjoy your summer!
References
American Association of Equine Practitioners (2016) Heat Stroke https://aaep.org/horsehealth/heat-stroke
Henderson, Brianne (2014) Part 2 – Developing the Sport Horse: the importance of hydration. https://www.equineguelph.ca/news/index.php?content=419#gsc.tab=0
Worldwide BioMedEx Inc. Heat-Stress Chart
NOAA’s National Weather Service Heat Index
Pritchard, Joy C., Whay, Helen R. (2010) Heat stress, climate change and animal welfare. The Vet Record, 166(25):798
Pritchard, JC., Barr, ARS., Whay, HR. (2006) Validity of a behavioural measure of heat stress and a skin tent test for dehydration in working horses and donkeys. Equine Vet J. 38(5):433-8
Pritchard, JC., Barr, ARS., Whay, HR. (2008) Validity of indicators of dehydration in working horses: a longitudinal study of changes in skin tent duration, mucous membrane dryness and drinking behaviour. Equine Vet J. 40(6):558-64
Pritchard, Joy C., Whay, Helen R. (2010) Heat stress, climate change and animal welfare. The Vet Record, 166(25):798
