If a horse works hard in hot or humid weather, he may suffer dehydration and exhaustion. Fluid loss (from sweating to cool himself) can lead to problems such as heat stroke, thumps (due to electrolyte imbalance) or dehydration colic. There are many ways you can help protect a horse from adverse affects of heat.
CONDITIONING – The fit horse, whose sweating and cooling systems are working well–with muscles working to best efficiency–is not as affected by heat as the unfit horse. If you begin workouts in early spring, you can have the horse physically fit before hot weather arrives. If he is already getting into shape by summer, he can adjust–and handle the heat–much more readily than a soft, fat horse being taken out for his first rides.
If conditioning a horse in hot weather, start slowly, gradually increasing the amount of work and length of rides. During a heat wave, avoid doing strenuous work during the hottest part of the day; ride early in the morning or late evening. Mornings are usually best–not as warm and humid as evenings.
Do strenuous work in short stints, alternating with periods of walking so the horse can stop sweating heavily for awhile. He can work longer that way, with less risk of heat stroke. Take time to warm him up before strenuous work. The increase in body temperature occurring during his warm-up will help prepare him for faster or harder work, since it increases the oxygen-carrying capacity of the blood vessels supplying his muscles.
LET HIM DRINK – On long rides, especially on hot days, let a horse drink as much water as he wants, at every opportunity. Drinking while working does not harm a horse (will not cause colic) as long as water is not ice-cold and the horse will be continuing exercise after drinking. He needs the fluid, and will be better off for it. The only time it’s riskly to allow a hot horse large quantities of water is if the water is very cold or if he’ll be standing around afterward. The blood supplying his muscles will then rush to the stomach to try to warm the large volume of cold water, leaving the muscles undersupplied with blood and causing muscle cramps and possible colic.
Any horse that is sweating should be allowed to drink as much as possible. Even the endurance horses that drink a lot along the trail develop slight to moderate dehydration on long rides in hot weather, but those that will not (or are not allowed to) drink very much suffer serious dehydration. Fluid losses of 6 to 10 gallons are common in endurance horses; the ones that compete successfully are usually those that continue to eat and drink at stops along the way, replacing most of their fluid loss by the end of the ride or early in their recovery period after the ride.
COOL HIM WITH WATER – The primary way a horse cools himself while working is to sweat, which produces cooling by way of evaporation. This uses up vital body fluids if he has to sweat for a prolonged period. On a long ride, you can help conserve his fluid resources if you periodically sponge him with cool water (such as every time you have access to water at a stream, pond, water trough along the trail, etc.) Endurance riders carry sponges and towels for this purpose, and it often makes a big difference in keeping a horse from dehydrating too much.
If weather is humid, sweat can’t evaporate as readily as on a dry day; he must sweat even more to cool himself. Horses are at much more risk for heat stress or heat stroke if humidity and temperature are high. Be aware of these risks and slow down accordingly – and help him out all you can. Also be aware that on a dry day his sweat may evaporate quickly, disappearing almost as soon as it forms. You may not think he is sweating much. He’s still losing fluid, however; if you help him out with added water sponged onto his body periodically, he’ll conserve his own supply.
USE SHADE/BREEZE TO ADVANTAGE – If you give him a breather during a hard workout, or a rest stop along the trail, try to find a place where there’s shade and/or a breeze to help cool him. Resting in the shade will be several degrees cooler than in the hot sun. Standing on a ridge where there’s some air movement will accelerate sweat evaporation and cool him more quickly.
LET HIM EAT GRASS – Whenever he sweats, he is losing body fluid and electrolytes. One of the quickest and easiest ways for him to replenish these is by eating green grass–which contains the needed electrolytes in proper balance, and also some moisture. At any rest stop during a long ride, let him graze, if he will. A tired and dehydrated horse will generally nibble green grass even if he’s not interested in hay. If a tired horse will eat, this is always a good sign.
PROBLEMS TO BE AWARE OF – Some horses develop dehydration colic during a long, hot ride. Even a horse that’s in good shape and drinking along the trail may still become seriously dehydrated if the day is very hot, humidity high, or the horse is using up a lot of nervous energy or sweating profusely. This type of colic is best treated with fluids (into the gut by stomach tube, and also intravenously – since the gut has lost ability to absorb fluids efficiently when the horse starts to get shocky). Mineral oil is not helpful in this type of colic and may do more harm than good. The horse doesn’t need lubrication in the gut as much as he needs fluid, and he needs it immediately, since he is suffering primarily from dehydration. If a horse ever starts to act colicky on a long ride on a hot day, and shows signs of dehydration along with slow or minimal gut sounds, fluids should be given as soon as possible by I.V. and continued until he is no longer dehydrated.
If a horse is already dehydrated and not drinking, do not give him concentrated electrolytes; this will only make the dehydration worse, pulling fluid from the body to dilute the concentrated salts. He must have fluid first.
Heat exhaustion may occur in a horse being overworked in hot weather, due to depletion of fluid and electrolytes, but an alert rider who knows his horse can sense the subtle signs of fatigue and dehydration before the horse is in trouble. If the ride is halted at the first signs of overwork, and the horse cooled down, the condition will generally not progress to the point of heat stroke or permanent damage.
A horse that’s starting to be in trouble will be depressed, with little interest in food or water. The horse suffering from heat exhaustion may continue to sweat, but at a reduced rate (he’s running out of body fluid to use for sweat). If he is severely dehydrated he’ll stop sweating. Pulse, respiration and temperature remain high in spite of a rest period. Pulse may be weak, heart rhythm irregular, intestinal sounds absent or diminished, and the muscles of the anus will be relaxed and floppy.
Overheating during work can produce serious medical problems, but by recognizing the early signs of distress the rider can halt the horse (and seek treatment immediately if the horse needs it), before the condition gets worse and the horse goes into shock. It’s best to avoid this problem with proper conditioning, careful and conscientious riding, utilizing as many ways as you can to conserve and replenish the horse’s body fluids.