The United States is experiencing a record-setting summer, with temperatures in the Southwest topping the 100-degree mark day after day. The suspects among the causes of this heat streak range from global warming to La Niña, none of which is certain. What is certain, however, is the effect of summer heat on horses.
Horses are much like humans in their response to the increase in temperature during the summer months. They generally respond to warm weather by sweating, just as humans do. And like humans, horses can endure a lot of heat if they are in good physical condition, have plenty of water, access to shade and, even better, a bit of natural or machine-generated wind. In a review of several studies on the effect of heat on horses, which was done in anticipation of the 1996 Olympics in Atlanta, Ga., researchers concluded that that there were clear physiological benefits produced from about 14 days of acclimatization to extreme heat. Racehorses that are based in the Southwest are, of course, already acclimatized to heat. And their trainers and grooms monitor their condition daily, provide plenty of water and keep their stalls cool with electric fans. The movement of air is important to horses because when they sweat, water rises to the surface of their skin. Once there, the process of evaporation provides some cooling. Evaporation alone is a relatively slow process. A bit of wind or a breeze from a fan increases the cooling effect dramatically.
On the days they race in hot weather, racehorses are usually given a cooling splash of water right after their tack is removed. Then they're led back to their barn to be walked until their body temperature returns to pre-race levels and they can be bathed. This cool shower, either from a bucket or a water hose, reduces the horse's body temperature quickly.
By taking care of one small but important detail, officials at Lone Star Park at Grand Prairie in Texas report that the horses are faring as well or better this summer than they did during Lone Star's inaugural meeting. According to Lone Star's Director of Media Relations, John W. Naylor, the track has added sources of water along the path that horses take going to and from the barns. (Incidentally, this summer Lone Star had added misters in various locations to make humans at the track more comfortable as well.) "In addition to the water hoses and ice that we have in place near the winner's circle to cool horses after each race," Naylor said, "we've positioned water hoses at 40-yard intervals between the test barn at the beginning of the stable area and the tunnel leading to the paddock. That means cooling water is available at 40-yard intervals from the backstretch, along the outside of the clubhouse turn and along the outside of about a fourth of the stretch-all the way to the point where they step off the track and go to the paddock.
"We've found this to be very important during the races too, as you might imagine," Naylor said. "After one recent race, our leading rider, Marlon St. Julian, found that his horse seemed a little bit wobbly. He got off immediately and led it to one of the hoses along the clubhouse turn. That cured the problem immediately. "
In general, Texas horsemen are experiencing a trouble-free summer according to Texas Thoroughbred Association Executive Director Dave Hooper. "I've spoken to Mike Burleson, who's the deputy director of racing for the Texas Racing Commission. He's in touch with the veterinarians at the tracks and he reports few, if any, problems related to this hot spell.
"I've also spoken with Dale Coleman, who's the stall manager at Lone Star Park," Hooper said, "and Dale said that the placing of additional water hoses this summer has actually caused horses there to have a better time of it. "
Even without cooling water, horses have an added advantage over humans during hot weather because the hair on their bodies will stand up slightly to create air pockets next to their skin. People can approximate this effect by wearing loose clothing in hot weather, but the horse has the system built in.
Despite every effort by human care givers to prevent it, horses can have their health seriously threatened by heat. Horses can be threatened by hyperthermia, which is called either heat exhaustion or heat stroke, just like humans can. Hyperthermia occurs when the horse's heat-regulating mechanism malfunctions. A horse affected by hyperthermia can be working hard, or moving under light exercise conditions, or can be in a stall. The most important factors in causing hyperthermia remain high temperatures and humidity coupled with poor ventilation.
When hyperthermia occurs, the horse's circulatory system begins to stall because its blood vessels begin to enlarge, in the process lowering the horse's blood pressure. That means the horse's body cannot dissipate heat as it must in hot weather. Of the two, heat stroke is more serious than heat exhaustion because heat stroke can lead quickly to death. That's the bad news. The good news is that both heat exhaustion and heat stroke are easily preventable, as long as humans are around to intervene with their common sense and knowledge of what's right for the horse.
Horses can also suffer from anhidrosis, also called dry-coat, which is the loss of a horse's ability to sweat. Anhidrosis usually affects horses that have been raised in temperate climates and moved to hot, humid climates. Horses that are raised in hot, humid climates seldom develop the disorder and not all horses are susceptible to it. The only way to prevent anhidrosis is to avoid hot, humid climates with horses that are susceptible.
In connection with the studies and trials done prior to the '96 Olympics, a number of cooling studies were carried out by various groups that indicated the benefits of "super cooling" by using large quantities of cool water. This would be applied by teams of two to four people using large sponges for 30 seconds, scraping the water off and walking the horse for 30 seconds and then repeating the procedure until the animal was effectively cooled. The post-race bath produces the same effect for racehorses, who may also stand in ice water to shrink the blood vessels in their feet. This increases blood circulation and helps the horse to get rid of its body heat.
Mostly, caring for horses in summer weather all comes down to common sense, an uncommon amount of real, everyday care and immediate professional help when all else fails. But most of all, that care still comes down to a human hand, a sponge and a bucket of cold water after a horse has run its race.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.