High summer temperatures can present problems for working horses. Temperatures above 80 degrees increase the risk for heat stress or heat stroke if relative humidity gets above 50%, with no breeze. Under these conditions, a horse has difficulty cooling himself, since sweat does not evaporate. One advantage in a dry climate and low humidity is that horses can usually cool themselves by sweating, unless they become dehydrated by having to sweat too much, too long.
Dr. Mike Foss, (Alpine Veterinary Hospital, Hood River, Oregon) says horses are more apt to become dehydrated in hot, humid weather than hot, dry weather. In a dry climate, sweat evaporates almost as soon as it is produced, reducing body temperature. If air is humid, evaporation is hindered. Sweat may cover the body and run off in streams or turn into lather as the horse’s fluid supply decreases. Without evaporation, the body won’t cool, and signals for more sweating. Sweat production increases, but does little good; the horse stays wet but does not become cooler. If he continues to exert or must sweat continually to cool himself on a hot day and cannot drink enough to replace the loss, he quickly dehydrates and overheats. The same amount of exertion in cool weather may not cause serious dehydration or heat stroke, but becomes a danger in the hotter, more humid days of summer.
Working/sorting cattle all day, riding range to check fences, gathering and moving cattle, etc. can take a toll in hot weather, especially if a horse is not in shape. Sometimes what you think will be an easy ride for a soft horse turns out to be longer or harder than you planned — if you discover cows in the wrong pasture and end up gathering, sorting and moving cows all day.
Foss says riders should pay close attention to the horse. If you know you’ll be out there working all day, pace your horse through the day so you don’t use him up too much in the beginning. Make sure he drinks enough to replenish what is lost through sweat.
“Give him a chance to drink at every opportunity. The old idea that you shouldn’t let a hot horse drink is not valid,” says Foss.
Unless the water is very cold and the hot horse will be just standing around after drinking, let him drink.
“Make sure he has access to salt in his pen or pasture, so he’s never short on salt. He’ll lose a lot of salt though sweating. On a hard ride he may sweat as much as an endurance horse — maybe even more, if he’s not in top shape. Also, most cow horses are more muscular than the typical endurance horse, with more body mass. Those heavy muscles create more body heat than lean muscles during exertion, and the horse’s body has to get rid of more heat,” explains Foss.
Dr. Martha Mallicote, with the University of Florida Large Animal Hospital, says horses are very efficient sweaters and quickly pull fluid from the bloodstream to put onto the skin through the sweat glands, to evaporate and help cool the horse.
“The sweat glands are already primed, all the time, with electrolytes, proteins and lipids, and all they have to do is draw water from the blood,” says Mallicote. “It doesn’t take long for sweat glands to recover and be prepared to produce more sweat.”
Horses that work hard in hot weather, if they are fit and in good condition, don’t lose as much fluid and electrolytes as an unconditioned, fat horse. Fit horses can keep going for miles and keep themselves within a normal range of body temperature.
“While you are riding in the heat, you just have to pay attention. If the horse starts puffing and has trouble catching his breath, let him slow down or stop and rest, and cool off,” says Foss. Otherwise you risk heat exhaustion.