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The Art and Science of Cooling Out
What's the right way to do it in terms of the events taking place inside your horse?
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Your horse has just finished a hard workout. He's blowing, and he's hot and wet. You're hot and tired, toobut your work isn't done yet. Before you or your horse can go off to rest, you'll have to make sure he's thoroughly cooled out. If you don't, you'll run the risk of serious troubledamage to muscles and perhaps colic or founder.
Many people follow traditional procedures to cool out their horses without really thinking about why they do it. Sometimes this leads to troublethe horse is put up when he's still hot or he's fed or watered improperly. A little understanding of the basic processes involved would help prevent such problems.
Cooling Out
To understand cooling out, you have to understand what went on inside the horse's body to get him overheated in the first place. As be began to work, his muscles started to burn more fuel for energy. The burning increased his need for oxygen, and it also created heat. In fact, only about a fourth of the energy produced in fuel burning went to move the muscles while the rest was released as heat.
Both problems were addressed by the horse's respiratory and circulatory systems. His nostrils opened to take in more air, and his rate of respiration increased to bring more oxygen into his lungs. At the same time, his heart increased both its rate and its output, beating more rapidly and sending out more blood with each beat. Arteries leading to the working muscles dilated and arteries leading to the stomach and intestines contracted so more blood went directly to the muscles.
The circulating blood did more than bring in oxygen. It also carried off the waste products of the muscles' fuel burning and some of the heat, too. From the muscles, the blood traveled to the heart and on to the lungs. There it passed through a network of tiny blood vessels where extra heat was lost to the incoming air and more oxygen was drawn in. Cooled and recharged, the blood passed through the heart once more and back to the muscles.
For some animals, such as dogs, the respiratory route provides the chief method of cooling. That's why dogs pant when they're hot. Horses pant, too, but in the horse increased respiration often is not enough. As your horse continued to work, heat built up in his muscles faster than his lungs could get rid of it. This buildup was monitored by the hypothalamus, the area of the brain that controls temperature. And in response, the hypothalamus brought several mechanism into play.
First, the hypothalamus signaled the blood vessels near the horse's skin to open wide. This caused more of the overheated blood to circulate near the skin where cooling air could draw off some of the heat. As long as he wasn't working too hard, this was enough to keep his internal temperature from rising out of control. But as he worked harderor if the outside temperature was high enough to lessen the air's cooling effectit was not enough.
Sweat glands in the horse's skin sprang into action. As the fluid produced by the sweat glands evaporated on the skin, it increased the cooling effect of the air. The horse began to sweat first around his head, neck and chest, so the evaporation was concentrated over the major blood vessels leading to and from the working muscles.
Now that you've stopped working, you can see all the signs of these processes. The horse is breathing heavily. If you check his heart rate, you'll find that it, too, is elevated. He's wet and you may see the dilated blood vessels standing out under his skin. But even with all these cooling mechanisms working full time, your horse's temperature, has probably risen above the normal range of 99 to 101 degrees.
How Hot is He?
Immediately upon dismounting, you should check your horse's pulse, respiration and (if possible) his temperature. By checking them again periodically as you cool him out, you'll get a picture of how seriously overheated he is and how quickly he's recovering. Because the levels of these measurements vary a bit from horse to horse, you should know your horse's normal level before you start work.
Count respiration by watching the flank move in and out with each breath. The resting rate varies from six to eighteen breaths a minute. Right after exercise your horse will probably be breathing deeply in an effort to replace the oxygen he used. But as soon as the oxygen debt is paid, he'll switch to a rapid shallow breathing pattern that keeps a steady stream of fresh, cool air coming into the lungs where it can pick up heat from the circulating blood.
Check the pulse by holding your fingers over the mandibular artery, which runs just inside each branch of the lower jaw. Count the number of beats in ten seconds and multiply by six to get the perminute rate. The resting rate is somewhere around 35 beats per minute. Depending on your horse's condition and the amount of work you did, exercise may send the pulse up to anywhere from 140 to 200. You should see it fall quickly, though, to 100 almost immediately and to its normal rate in fifteen minutes or so.
The respiration and pulse rates together give you a general rule of thumb for telling how hot your horse really is. When the respiration rate is higher than the pulse rate, you know he's overheated because he's panting rapidly in an effort to cool off. While both rates should slow significantly during the first few minutes of cooling, within five or ten minutes of stopping exercise the respiration rate should fall below the pulse rate. If your horse is still panting at this point, you know the overheating is serious.
Taking the rectal temperature will also give you an idea of the severity of the problem. Brief exercise can easily send the temperature up to 103 degrees; sustained exercise to 104 or 106, which is seriously high. What's more, studies have shown that the rectal temperature after a prolonged workout may be two degrees lower than the temperature in the muscles themselves, so a horse with a rectal temperature of 105 might be a very hot horse indeed.
One yardstick you can't use is the amount the horse is sweating. This varies not only with the weathersweat evaporates faster when the humidity is low, so you can see less of itbut also with the horse. Some horses suffer from a condition called anhidrosis and sweat too little or not at all. In this case, the horse that isn't sweating may actually be hotter than the one that is because he doesn't benefit from the cooling effect of evaporating moisture.
Walking
Your first step in cooling out is to get off and start walking your horse. In fact, take the pulse and respiration readings on the move or while pausing for just a few seconds. It's critically important to keep the horse moving because you want to keep his circulation going.
The horse's heart rate will start to drop rapidly the minute hard exercise stops, b ut you don't want it to fall to its resting level too quickly. For one thing, the circulating blood is helping to cool the overheated muscles and also to clear out toxins that have built up as a result of fuel burning. For another, his blood vessels are still dilated. If the pumping action slacks off too sharply, the blood will tend to pool in the dilated vessels and in the lower legs rather than completing its route through the body. That means that other body areas won't get enough blood. It's this phenomenon that causes human athletes to faint if they stop hard exercise too abruptly. In the horse, it could lead to muscle stiffness, fainting and cramping.
Mild exercise, such as walking, prompts the heart to keep pumping at a slightly elevated rate, and the contractions of the muscles themselves also help to move the blood along. If it's a hot day, do your walking in the shadethe hot sun alone can raise a horse's temperature by a degree or two. And if there's a breeze, walk in big circles so that the moving air reaches all sides of his body.
Horsemen have a lot of different theories about when to remove tack and when to put a cooler on the horse. Basically, the theories boil down to differences of opinion over the effect of cool air on the horse's overheated skin. Some people feel that a sudden shock of cool air will cause blood vessels near the skin to constrict, reducing the flow of blood to the surface and perhaps causing the muscles to cramp, but unless the air is much below 60 degrees you don't need to be too concerned about this. The blood vessels are dilated because of internal processes, not because of air temperature, and they'll probably stay dilated until the horse cools off. And, if you immediately cover the horse or keep his tack on, you lose some of the benefit of circulating air.
So after a couple of minutes you can probably pause in your walking to remove the horse's tack. But in very cold weather, you might loosen the girth and leave the saddle on for ten minutes or so. Loosening the girth will at least allow him to be more comfortable and it lets a bit of air under the saddle. For the same reason, a cooler may not be necessary except in very cool weather. If the temperature is much below 60 degrees, though, a cooler may help keep the skin and surface muscles from becoming chilled too rapidly. Unlike a fitted blanket or sheet which lies close to the skin, a billowy cooler allows some air to circulate underneath while it protects the horse from the full force of wintry blasts. Various styles are available: openmesh weaves allow more air to circulate while traditional wool types provide more protection. There are also wool coolers lined with mesh (similar to the practice of putting on two coolers) that are said to offer the advantages of both. In any case, a cooler won't cool your horse out for you. You'll still have to walk.
Sponging and Hosing
As your horse's temperature begins to drop, he will stop sweating. That means you'll lose the cooling benefits of evaporating moistureunless you create some artificial sweat for him with a hose or a sponge. A horse that suffers from anhidrosis and doesn't sweat enough will need your help here even more.
Water has two effects. Applied directly over the blood vessels, it helps cool them immediately. This effect only lasts a minute, though; once water is on the skin, it quickly heats to body temperature. That's where the second effect comes in. The water begins to evaporate and, just like sweat, increases the cooling effect of the air.
There are a lot of different theories and practices when it comes to hosing or sponging a hot horse. One school says to apply water only over major blood vessels at the head, neck, chest and inside the hind legs. The idea is that wetting the horse all over will cause his blood vessels to contract. Less blood will travel to the surface to be cooled, and the muscles may cramp because they're not getting enough blood.
If the horse is only moderately overheated and the outside temperature is cool, this method is fine. But if the horse and air are warmer, you might do better to dampen the horse all over with a sponge or with a fine mist from a hose. No research indicates that the blood vessels really do close; it's more likely that, since internal heat has prompted them to open, they'll stay dilated as long as the horse is hot. And the light dampening will give the horse the cooling benefits of evaporation all over.
Similarly, there are different schools of thought on what temperature the water should be. Some people believe the water should be tepid or even warm, so as not to shock the horse and send his muscles into cramps. But again, this depends on how hot the horse is and what the weather is like. Dousing a horse with warm or tepid water on a hot, humid day won't do as much good as using cool water: warm water won't give you the first benefit, that of cooling from initial contact, and on a humid day evaporation will be less.
As a general rule of thumb, you can figure that if the horse's temperature is under 103 and the air temperature is under 70, you probably won't need water to cool him off. If the day is warmer70 to 80 degreessponging the crucial areas may suffice. And if it's over 80, an all over sponging or mist from a hose can't hurt.
When the horse is really hot--with a temperature of 104 or more, for example--you'll probably want to use water. If the air temperature is under 60, sponge the crucial areas and then cover with a cooler. (Hosing all over and then covering the horse would defeat the purpose of using waterthe cooler would slow evaporation too much. But the cooler will still allow plenty of air to circulate around the neck, chest and between the legs.) Sponging should do the trick on 60 to 70 degree days, while an over dampening will help on the hottest days.
As far as water temperature goes, the hotter the horse and the day, the colder the water can be. If the horse and the day are very hot, you can use very cold water--even ice water--to help him cool down quickly. When the horse's temperature is up around 105 or 106, you want to cool him off as fast as you can. (In fact, if you have a stream or a pond handy, it's a good idea to walk him right into it, so he'll have a steady flow of cool water over his hot muscles.) But even if he's not that hot, the water you use for sponging or hosing should always be cooler than the horse is.
The time to sponge or hose varies, too. Unless he's severely overheated, you can walk for a few minutes and then pause to dampen him down after his heart and respiration rates start to slow down. But if he's very hot, you won't want to stop your walking even for this. Have an assistant walk with you with a bucket and a sponge, dampening your horse on the move.
You should repeat your hosing or sponging as you walk, giving the water a chance to evaporate and then reapplying it until the horse's temperature get closer to normal, say about102. At this point, he's pretty nearly cooled out. Walk a bit more the let him dry and to give his temperature a chance to go all the way back to the normal range. Since the rectal temperature is often lower than the muscle temperature, a reading of 102 could mean that his muscles are still at 104.
Drinking and Eating
Once the temperature, pulse and respiration start to drop, you can pause every so often in your walking to let your horse sip water. He's probably thirsty because he lost body fluids while sweating. If he did prolonged work, the loss may be large enough to be a contributing factor in the heat he's feeling now. The moisture he lost through sweat was drawn from his blood supply, leaving a lower volume of blood to circulate and help cool out the tissues, so it's a good idea to let him start replacing what he lost.
Along with causing fluid loss, severe work will also drain your horse's reserves of electrolytes. If you have an electrolyte solution handy, now would be a good time to offer it. Make sure that you continue to offer plain water, toosome horses will object to the salty taste of the solution and stop drinking altogether, and they won't replace their lost fluids.
But too much cool water too fast can lead to trouble. Remember that in work the arteries leading to the muscles dilated while those leading to the stomach contracted. Right now, the stomach is undersupplied with blood and is not ready for a big delivery of anything, even water. If you let the horse have his fill of cool water now, he could easily drink enough to distend his stomach and set himself up for a bout of colic. Blood would also rush to the stomach and leave the muscles undersupplied, which would hinder the cooling process and might also provoke cramping. A safe rule is to allow five sips for every fifty yards you walk.
For the same reason, you should hold off feeding your horse until you're sure he's completely cooled out. It's okay to let him have a few mouthfuls of hay or grass as you walk. If he did hard work, he'll appreciate ithe's probably ravenous. And the small amounts of hay or grass will help get his gastrointestinal tract back in operation gradually. When you put him back in his stall, you can leave some more hay.
How long you should wait before giving grain depends on the horse and the circumstances. If he's done a routine amount of work at a time of day when he usually works, and it's now time for his regular feeding, you can probably go ahead. But you should wait for an hour or two to feed grain if he's had unusually heavy exercise or if you disrupted his schedule by, say, giving him a late afternoon workout when he usually works in the morning. Giving a half ration is also a good idea to avoid overloading the digestive system if it's not fully operational yet. Certainly you shouldn't give the horse an extra feed of grain after work. That's asking for trouble.
Back to the Barn
How long it takes your horse to cool off depends on a lot of factorshow hard he worked, what his overall condition is, the temperature and humidity of the day and even his build. The more chunky he is, the longer it will take to cool him out because a chunky horse has more mass behind every square inch of skin. All the bulky muscles are holding heat that will have to be released through the surface before his temperature will drop.
Cooling out may take anywhere from twenty minutes to an hour. Rather than setting a time and assuming that your horse will be cooled out after so many minutes, use the temperaturepulserespiration yardstick as your guide. When everything's back to normal and he appears to be comfortable, it's probably safe to put him back in his stall. A gentle rubdown on his legs will help the circulation and ease any muscle stiffness. Now that you're sure he's cool, you can switch his cooler for whatever sheet or blanket is appropriate for the weather.
Don't leave him with a full water bucket unless you can see that his initial ravenous thirst has fadedthat way you can be sure that he won't drink too much at one time. And don't go away. He may feel cool to the touch, and his rectal temperature may be normal, but his muscles could still be harboring head deep inside. As he standing in his stall, his circulation will slow and the muscles will stop cooling. Pretty soon he'll break out in a sweat again.
For this reason, it's a good idea to go back fifteen minutes or so after you've put him away and check his temperature again. If you find that he's hot or sweating, take him out and walk some more until he's cool again. Repeat your check after you've put him up.
When a horse has done hard work, it's also a good idea to check on him several hours later. Two serious problemscolic and laminitisoften follow heavy exercise. Traditionally, improper cooling out has been thought to be a factor in both. But since the causes of these ailments are still somewhat mysterious and poorly understood, how much of a factor it is is anybody's guess.
A horse can experience mild abdominal discomfort after exercise simply because he's hungry and thirsty. Once he's cooled down, the bulk of the blood flow will shift back to the gastrointestinal tract, where it usually goes when the horse is resting. The blood flow prompts peristalsis, the rhythmic contractions of the stomach and intestine walls that move food along. If there's nothing inside to move, the horse feels hunger pains. On the other hand, if he's been allowed too much food and water at one time, his colicky signs may stem from a distended abdomen.
The relationship of laminitis to cooling out is somewhat more tenuous. When a horse develops laminitis after hard work, concussion is the first cause to be suspected. It's possible that, if the horse isn't properly walked out right after work, the pooling of blood in the lower legs may have a contributory effect. Similarly, if the horse has become severely dehydrated during work and, therefore, has a lower volume of blood, he'll have changes in circulation and also in coagulation that can contribute to laminitis. You can check for dehydration by picking up a fold of skin and releasing it; if the skin stays wrinkled for a moment rather than snapping back in place, the horse may be dehydrated. |
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[NOTE: Author and source unknown.] |
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