For longer than anyone can remember, horsemen have been warned that watering off a hot horse too quickly can be dangerous. In his classic how-to manual Training Thoroughbred Horses published in 1953, Racing Hall of Fame trainer Preston Burch wrote: “A horse is very easily foundered by too much water or feed at this time … Three or four good swallows of water may be given to him every two or three rounds of the walking ring, or every time around if he is walking around a big stable … The procedure for cooling out a horse after a race is the same as when he has taken a serious workout.”
No scientific evidence supports this practice. In fact, two experts said a horse needs to rehydrate promptly after exercise to allow its body's cooling mechanism to function effectively. And this is especially true if the horse is receiving the diuretic furosemide (Lasix). As long as the water is not ice-cold, let the horse drink as much as it wants, as soon as it wants.
“Two things a racehorse is dealing with, particularly after a race, is heat — getting its body temperature to cool off — and dehydration, particularly if it's had Lasix,” said Dr. Gary Potter, professor emeritus in animal science from Texas A&M University. “A horse has to sweat; it's their basic mechanism to dissipate heat. In order to sweat, they have to have plenty of water in their system, particularly their gut, which is a reservoir for water. So they need to drink as soon as they can to rehydrate themselves.”
In the cooling process, blood is shunted through dilated veins and capillaries close to the skin surface in an effort to cool the blood coursing through them. When wind blows across sweat on the skin surface, heat is drawn out of the horse and lost to the air as the sweat evaporates. The horse must have enough water to produce sweat and to replenish the water lost via sweat.
Potter said he understands that some horsemen may worry about allowing a horse to drink its fill when it first comes off the track, but as long as it is watered off within the first 10 to 15 minutes, the horse should be able to cool out normally.
“Particularly if they've had Lasix, they are severely dehydrated and significantly hot internally, and they need to get as cool as they can and as quick as they can for a lot of reasons,” he added.
Heat and dehydration adversely affect muscles, blood flow, and nerve function. In extreme cases, death can result from hypovolemic shock or cardiac arrest.
Potter dispelled the myth that a horse can rupture its stomach by guzzling a whole bucket of water too quickly. A typical Thoroughbred's stomach capacity is three to four gallons, and ingested water starts passing down through the gastrointestinal tract almost immediately, so no such danger exists.
Dr. Jonathan Foreman, professor of large animal medicine at the University of Illinois at Urbana-Champaign, conducted extensive research during the 1996 Olympics on the proper way to cool out a hot horse. He found that two accepted practices actually are detrimental: not scraping off the water after hosing down a hot horse and the use of a cool-out sheet. Both practices interfere with the horse's ability to dissipate heat through sweating.
“One of the key things is to scrape the water off frequently so that it doesn't just sit there like a hot, insulating blanket,” he said.
A cool-out sheet, which becomes wet and hot soon after it is draped over the horse, also holds in heat. Don't use a cool-out sheet; allow the horse's sweat to cool it naturally, he advised.
When bathing a hot horse, Foreman recommended using very cold water. He said the adage that cold water on hot muscles will cause the horse to tie up is not true. Studies looked at horses bathed in water of ambient temperature and those bathed in very cold water.
“There was no difference in those two groups afterward in terms of muscle enzymes, no evidence of tying up,” he said. “In fact, the group with the colder water did cool off faster. … Even ice-cold water when you put it on, by the time it runs around the horse's belly is very hot. And that's going to act as a hot-water blanket unless you scrape it back off.”
Regarding watering off, Foreman said horses essentially limit themselves because a horse can't drink water and breathe at the same time. A horse coming off strenuous exercise has a fast respiratory rate, and it only will drink until it needs to take a breath.
“If a swallow is 150 milligrams, then a gallon is 25 swallows,” he said. “Most horses, if they're still breathing hard, won't drink 25 swallows because at some point, they have to pull their head out of the water to catch their breath. They are just not in any real danger of overdrinking after exercise.”
No Fancy Electrolytes
Don't put electrolytes in the horse's water, Potter said.
“If you get the electrolyte concentration in the horse's water too high, it will discourage the horse from drinking. The best way is to put the electrolytes in the feed trough,” he said. “But in my description of electrolytes, we're talking about salt. You don't need the complicated electrolytes that have sugar, amino acids, and all that stuff — just plain sodium chloride.”
Potter advised horsemen to place a handful of salt in the horse's feed tub, separate from the feed, with each meal. Do not mix it through the feed because too much salt will discourage the horse from eating. In his research, Potter found the optimum amount of salt per day for the average horse is 90 grams, or roughly three ounces, in addition to the minimal amount contained in commercial feed. He discourages horsemen from providing a tub of free-choice loose salt in the stall because he said some horses may develop a psychological salt addiction, which may cause physical problems.
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