Heat Stroke Havoc: Horses and Cows and Pigs, Oh My!

“Heat stroke? Horses get that?"

July 22, 2013 (published) | June 20, 2023 (revised)

spraying-horse-faceIt’s pretty hard to accidentally lock your horse or cow in the car.

Small animal veterinarians, humane societies, and even municipal police and fire departments have done a great job of reminding folks that car = greenhouse/oven and car + warm day + dog or cat = baked pet. Yet, for most people, that seems to be where the link between animals and heatstroke ends. Somehow, in the public mind, a car-external animal is magically free of all heat-related danger.

I think we may be victims of our own PR, or rather our animals may be the unintended victims of this small, but effective, snapshot of heat stress.

Here’s a slightly different picture of heatstroke – no broken windows involved…

It was the sort of puffy April day made for Easter cards. Before I removed the rapidly rising thermometer from my shaking, flared-nostril patient, I knew the sort of response I was going to get as soon as I made my diagnosis.

“Heat stroke.”


“He has heat stroke; can you turn on that hose over there?” I had already moved the horse into the shade for the examination.

My client, an experienced, educated horseman was nonplussed. “Heat stroke? Horses get that? But it’s only about 80F out.”

“Yep. Heat stroke.” I showed him the thermometer which had topped out near an impressive 107°F (a normal horse resides in the 99-101°F range). “We need to cool him down. Ummmm…the hose?”

Heat stress – also known as heatstroke, heat exhaustion, or more officially hyperthermia – happens when an animal either produces too much heat or doesn’t dissipate (get rid of) enough. The dog-in-car case is an example of a failure of dissipation. Temperatures rise in the enclosed environment and the normal methods of heat dissipation (i.e. panting) don’t work since there is nowhere for the extra heat to go. In healthy animals not receiving medications or carrying genes that may predispose them to hyperthermia, excess production usually results from excessive activity.

“But aren’t animals smart enough not to over-do it on a hot day?”

Ummmm…. Met any human long-distance runners lately? Humans aren’t smart enough not to work ourselves into heat stress (card-carrying member of the Stupidly Prone to Overdoing it on Warm Days League here), and neither are our four-legged friends.

The horse with the Death Valley worthy temperature had demonstrated a classic disregard for his own well-being. The owner, taking advantage of the lovely weather, had turned the normally barn-housed young stallion out for a nice romp in the front paddock. Spring is breeding season in the equine world and this young lad could smell all sorts of lovely ladies. The horse equivalent of an early-20s human male, he responded just as his human counterparts would: by showing off.

For two hours, the stallion ran himself silly, bucking, prancing, and bugling to any mare within the county limits. He did not stop for water in his corral, nor did he seek the shade that was at one end of the corral.

A dog turned loose in the dog park or on a beach on a deceptively warm day can run (literally) into the same trouble. Rarely did I ever treat heat stress cases in July or August when sidewalks in our region are made for egg-cookery. Like humans, animals tend to mope around looking for air-conditioning and ice cream when the mercury bursts from the top of the thermometer. It’s the first warm days of spring you have to watch out for.

Even outside the solar-cooker that is an automobile, heat dissipation can become seriously compromised for many animals.

Animals cool their bodies through water evaporation from: sweating (horses), panting (dogs), or soaking themselves in water (pigs). On high humidity days, the cooling effect of evaporation is lost or at least significantly diminished. Adding in even a little extra heat production on those days can precipitate a hot mess.

Dark-coated animals (such as black Angus cattle) or animals with thick fleeces are also at a disadvantage in the heat dissipation game. The “down” (i.e. can’t get up because she’s sick or her foot is injured) black cow, the un-shorn sheep, or heavily fleeced male llama are all heatstroke victims who have crossed my clinical path. Black cows are not quite as unlucky as black cats when it comes to path-crossing unless they step on your toes.

Pity the pig. “Sweating like a pig” is not only an exaggeration. It’s an out-and-out lie. Pigs don’t sweat. They can’t sweat. They don’t pant particularly well either. So, for Wilbur and friends, heat dissipation requires cooperation from their environment. “Happy as a pig in mud” isn’t an exaggeration. Pigs wallow in mud or water in order to cool themselves, not because they have the same aversion to cleanliness as my kids. Pigs need a pond, pool, or misters and fans in order to properly dissipate heat. Since pigs can’t self-cool, it’s important to consider temperature and ventilation when transporting them. The client who brought a pig to me one day for a pre-fair health check nearly had a baked ham by the time he opened the door of the non-ventilated cargo hauler that he had decided to use as a swine-mobile. (We were able to treat the pig in time, and I advised the owner that pigs have different transportation requirements from dirt bikes.)

Just about any animal is susceptible to heat stress; even fish can poach if their bathwater warms. So how can you prevent heatstroke and how (leaving fish out of it) do you recognize signs of heat stress?

Prevention of heat stress is a matter of monitoring the balance between heat production and heat dissipation.

Obvious steps like making sure the animal has access to water and shade – yes, even if you’re just at the dog park or riding your horse for a couple of hours – are important, as is verifying that said animal can reach said water or shade. Shade, especially, tends to move. A horse tied to a trailer in the shade at a show may not stay in the shade, ditto for a dog tied to a tree, stake, picnic bench, etc.

Monitor exercise closely, especially if the weather is warmer than usual, the animal is overweight or out of condition, or there are factors, such as in-season mares, that may cause the animal to exercise more vigorously than normal.

Plan transportation for cool times of the day. This should go without saying, but do NOT leave animals in an enclosed, non-air-conditioned vehicle. Even stock and horse trailers with open vents/windows can get very, very warm when not moving (large aluminum box + heat-producing animals).

Shearing fleeced animals in spring can minimize heat stress, not to mention reducing disturbing fly/maggot antics that tend to accompany warm weather and soiled fleece. (Don’t ask.)

Signs of overheating vary a little between species, but here are some basics:

  • Profuse sweating (and/or a suspicious lack of sweat) – in people and horses
  • Rapid breathing – pretty much all mammals
  • Panting – dogs, cats, cattle, sheep, goats (yes, the latter three can look like they are panting, and yes, it’s disturbing)
  • Flared nostrils – horses, cattle, sheep, goats, llamas
  • Shaking muscles
  • Bright red or very pale mucous membranes (gums, insides of lips, insides of nostrils, inside of vulva)
  • Signs of exhaustion – head down, no interest in food or water, lack of response to stimulus
  • Decreased/very concentrated urine
  • Elevated body temperature
  • Elevated heart rate. If you don’t already know, ask your veterinarian to teach you how to check normal vital signs (temperature, heart rate/pulse, and respiratory rate) for your animal(s).

Heatstroke causes as much havoc in the body as my 8-year-old can wreak in her bedroom with a couple of friends and a free afternoon. Kidney failure, clotting disorders, brain damage, death – these aren’t bit players in the pageant of life.

Definitely don’t leave your pet in the car, but think also of the running horse, the Frisbee-catching dog, the wooly sheep, the invalid cow, and the puddle-less pig. Any animal, yes, even those who live in the great outdoors, can over-do a day in the sun.

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