Heat Index and Riding - The Horse Forum
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post #1 of 16 Old 07-21-2011, 01:42 PM Thread Starter
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Heat Index and Riding

I do think I've seen it posted here in past, so apologies if I repeat. Got it today on my local forum, so want to share... :)
Summer riding reminder

The Heat Index is the sum of the temperature plus the humidity.
For example:if the temperature is 80 degrees Fahrenheit and the humidity is 20%, then the Heat Index is 100 (80+20=100). If the Heat Index is less than 120, it is ok to ride. Start watching it as it rises above 120, at 150 your horse's cooling system won't work effectively. If it is greater than 180, your horse will be unable to thermo-regulate.

When is it too hot to safely ride my horse?

Written by: Sallie S. Hyman VMD, DACVIM, CVA

Knowing how your horse thermo-regulates will help you better understand how to keep him cool. A horse's body produces heat when he works. Horses have several mechanisms that get rid of this heat.

The most important mechanism is evaporation. Most heat is generated from a horse's large muscle mass. The cardiovascular system (the heart and blood vessels) move the heat from the muscles and organs to the skin. As your horse works, he produces sweat in glands in his skin. This sweat is composed of water and electrolytes (sodium, chloride, potassium, and calcium). As the sweat evaporates, it dissipates large amounts of heat, thus cooling your horse. To give you an idea of how much a horse needs to sweat to keep cool, the amount of heat dissipated by one liter of sweat equals just one to two minutes of maximal exercise, or five to six minutes of sub maximal exercise!

Signs of Heatstroke in Your Horse:

  • A Respiratory Rate Higher than 30, that does not return to normal after several minutes of cooling off
  • A Heart Rate Higher than 80, that does not return to normal after several minutes of cooling off
  • Excessive sweating, or ceasing to sweat at all
  • Temperature of more than 103į F, that does not decrease after several minutes of cooling
  • Depression/Lethargy
  • ďThumpsĒ - diaphragmatic flutter due to calcium loss. You will see this as twitching of the stomach area.
If you see ANY of these problems, cool your horse with plenty of cold water, allow him to drink if he wants, and call your veterinarian! You can give paste electrolytes orally as well, such as Neogen Stress-Dex Gel or Summer Games Electrolyte Paste. Your veterinarian will decide if IV fluids and electrolytes are needed.

Horses who do experience heatstroke should be rested for ten days and given a few days of light work before being brought back to normal work. Keep in mind that horses that experience overheating are more prone to do so again, so best to prevent it in the first place!












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post #2 of 16 Old 07-21-2011, 01:45 PM
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Thanks for the info.
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post #3 of 16 Old 07-21-2011, 02:32 PM
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If I'm going to ride in midday, I only walk. That never seems to do any sort of damage-she's still eager and bright-eyed afterwards, and the only places she sweats are under the tack areas.

I do all my trotting and cantering work at sunset, though.
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post #4 of 16 Old 07-21-2011, 02:56 PM
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Heat index of 120 seems a little high before being cautious, doesn't it? It's reported to be a heat index of 105 - 107 today in eastern PA. Althought, it might be a different calculation than what's stated above. The temp is reaching 100 degrees and the humidity is 42%, so that would be a heat index of 142 according to the calculation above. I just checked the heat advisory warnings from the national weather service, and they are reporting heat index as 105 - 110.

Just be aware that your news reports may refer to the heat index as different calculations...

Kelly
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post #5 of 16 Old 07-21-2011, 04:20 PM
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Quote:
Originally Posted by kitten_Val View Post
Summer riding reminder

The Heat Index is the sum of the temperature plus the humidity.
For example:if the temperature is 80 degrees Fahrenheit and the humidity is 20%, then the Heat Index is 100 (80+20=100). If the Heat Index is less than 120, it is ok to ride. Start watching it as it rises above 120, at 150 your horse's cooling system won't work effectively. If it is greater than 180, your horse will be unable to thermo-regulate.

The formula for figuring out the heat index is actually very complicated. You do not just add the temp and the humidity. I copied and pasted the formula for figuring out the head index. as you can see it is far easier to go to weather.com where the have it already set up. All you have to do is enter the temp and humidity and then hit "calculate".

where
= heat index (in degrees Fahrenheit) = ambient dry-bulb temperature (in degrees Fahrenheit) = relative humidity (in percent)
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post #6 of 16 Old 07-21-2011, 04:28 PM
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Thanks KV! I was just thinking about this today!

Quote:
Originally Posted by wetrain17 View Post
[/INDENT][/INDENT] where
= heat index (in degrees Fahrenheit) = ambient dry-bulb temperature (in degrees Fahrenheit) = relative humidity (in percent)
OK, but looking at that formula, KV's estimation (key word being estimation) really shouldn't be that far off given that c1-c8 are constants and the equation itself appears to be logarithmic? As is (roughly) the mathematical relationship that KV describes?

Just a thought

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post #7 of 16 Old 07-21-2011, 04:32 PM
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May I just say I now have a headache that has nothing to do with the actual heat index and everything to do with reading that formula? HAHAHAHAHA
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post #8 of 16 Old 07-21-2011, 04:34 PM
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Quote:
Originally Posted by sarahver View Post
Thanks KV! I was just thinking about this today!



OK, but looking at that formula, KV's estimation (key word being estimation) really shouldn't be that far off given that c1-c8 are constants and the equation itself appears to be logarithmic? As is (roughly) the mathematical relationship that KV describes?

Just a thought


...uh...


What?
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post #9 of 16 Old 07-21-2011, 04:37 PM
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Quote:
Originally Posted by pintophile View Post


...uh...


What?
Heh. Nerd status of Sarah: CONFIRMED.

Basically I think that KV's estimation holds reasonably true to the model

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post #10 of 16 Old 07-21-2011, 04:39 PM
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That is good to know. It is hard to ride them when they are sweating standing still, but I have a couple that really need to get back in shape and I was just wondering at what point I should not ride. Thanks!
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