Protecting Horses in Heat Waves

There is no question climate change is here and we and our animals are being subjected to steadily increasing extreme heat. Managing this is challenging. 

The first question is, and should be, can I work my horse in the heat. A heat index chart can be found here. Caution should be used above a heat index of 80. From 90 to 102, overheating occurs easily. Above that level, I do not recommend exercising the horse. During a heat wave, you are most likely to find a window of opportunity around dawn or even at night.

Even horses not being actively worked are at risk of dehydration with consequences like impaction colic. Young foals, overweight horses, and very old horses, especially those with Cushing's/PPID, are at the highest risk for overheating.

Dehydration begins with salt depletion. The body requires salt to hold water in the tissues and the brain reads salt concentrations to tell it when to start water conservation through reduced urine output, and when to trigger thirst. Salt depletion is a consequence of both inadequate intake and losses in sweat. 

Adult-size horses should get at least 2 ounces (4 tablespoons) of salt water in hot weather, more if they are visibly sweating - e.g. along the chest, under the mane, and between the hind legs. Add another half ounce for lactating mares. Adjust down for smaller animals.

For horses being worked in the heat, feed one dose of balanced electrolyte (PFL Pro-Lyte Pellets) for each hour of heavier sweating (count sweating during cooldowns. IMPORTANT: This is in addition to the 2+ oz of salt fed at baseline.

Do not rely on consumption from a block to meet needs. Horses' bodies often become salt depleted quickly then "reset" to maintain blood sodium levels at the expense of the tissues. When this happens, the brain thinks everything is normal but the horse is actually dehydrated.

If the horse won't eat the required amount mixed into feed, you can sprinkle it onto moistened hay. A quick dunk or spray will do. You can also offer salted water, up to 8 tsp/gallon, but only if the horse also has an unlimited supply of fresh water.

Speaking of fresh water, a problem with automatic waterers can be disastrous at this time, especially if you do not have meters on your waterers. Contact the manufacturer for advice on maintenance. This article from a manufacturer gives some ideas on what is involved in maintenance. Be particularly careful with new horses not accustomed to using them.

Early signs of dehydration include:

  • reduced urine production
  • drier manure
  • sticky feel to the mouth
  • abnormal skin pinch test (watch video here)
  • reduced exercise performance/"hitting the wall"

The skin pinch is the most popular test but is unreliable in older horses, horses with DSLD, and under very dry environmental conditions. 

It is a myth that you shouldn't hose a hot horse with cold water. In fact, the colder the better. Also, be sure to scrape off the water after you are finished or it will actually prevent heat from escaping. 

There should always be shade available and fans if possible. Misting fans are best.

It's a lot to think about but your horse's health, even life, depends on proper care in the heat.

- Eleanor Kellon, VMD

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