Heat Exhaustion

Exhaustion occurs in most equestrian sports, but it is more frequent in events that require sustained endurance work such as endurance racing, three-day eventing, trial riding, and hunting. Exhaustion is also more likely when an unfit, unacclimatized, or unsound horse is exercised. Mechanisms that contribute to exhaustion include heat retention, fluid and electrolyte loss, acid-base imbalance, and intramuscular glycogen depletion. Clinical signs include elevated temperature, pulse, and respiratory rate; depression; anorexia; unwillingness to continue to exercise; dehydration; weakness; stiffness; hypovolemic shock; exertional myopathy; synchronous diaphragmatic flutter; atrial fibrillation; diarrhea; colic; and laminitis. Treatment includes stopping exercise; rapid cooling; rapid large volume intravenous or oral fluid administration; and nonsteroidal anti-inflammatory drug administration.

Horses that are inadequately trained or have other systemic or musculoskeletal problems or those that are competing in hot conditions may develop a variety of metabolic problems. It is hoped that knowledge of the fluid and electrolyte losses may help in treating horses with metabolic problems and, more importantly, in improving management of horses in training and competition to prevent any loss of performance.

It happens often at endurance races and is, therefore, commonly viewed as a problem of the endurance horse. But heat exhaustion happens in polo ponies, steeplechasers, eventers, trail riders – any horse exerting himself for more than just a quick sprint, and particularly when it’s hot and humid outside. At endurance races, the scenario is common to the point of being a stereotype: one of the horses has been pulled from the race for failing to recover adequately during a vet check, and now his condition is worsening despite several minutes of rest, and suddenly the reality hits his worried owner like a freight train: his horse might not make it. The event’s on-site veterinarian is summoned, and the drama unfolds.

But what if your horse is stricken and you’re at an unsanctioned event, where there’s no veterinarian available? Or you’re on a training run, rather than at an official event? Or it wasn’t intentional exercise at all – your show horse somehow got out of his stall and has been running, terrified, with snarling dogs at his heels, for the past hour as the outside thermometer creeps up to 95°F and the relative humidity is close behind? What do you do?

What You See

The hallmark of advanced heat exhaustion is lack of interest in eating or drinking after a workout, despite the absolute certainty, after the rigors of his exercise, the horse desperately needs the liquids and electrolytes that water and food would provide. The full list of signs includes:

  • shortened stride, lack of impulsion
  • elevated rectal temperature (as high as 104-107° F
  • depression, acts profoundly tired
  • inattention:shows no interest in surroundings
  • unstable or persistently elevated heart rate
  • persistently elevated respiratory rate, or panting
  • the “thumps” (what appears to be a rhythmic jerking of the abdominal muscles with each breath, almost like violent hiccups)
  • no appetite, no desire for water
  • glazed look in the eyes
  • “quiet gut” – the normal motility of the intestines has slowed
  • sweat-soaked or less than expected sweating
  • scant and very concentrated urine

The goal in dealing with this dangerous condition is catching it in its earliest stages, before the diagnosis is obvious and before the horse’s cardiovascular system breaks down.

Why Is Heat Exhaustion Dangerous?

This is much more than just a bad case of fatigue. It’s a dangerous buildup of heat in the horse’s body which, if unresolved, can lead to cardiovascular instability, collapse and death.

It is caused by electrolyte deficits in the exhausted horse that can be astounding, and since the sensation of thirst is linked to the detection of excess salt in the system, the salt deficient horse feels no desire to drink. This means that, if left to his own devices, he would be unlikely to recover because despite his dehydration he has no natural urge to replace the liquids he so desperately needs.

To naturally replace electrolytes, the horse must eat. However, of his mineral deficiency is severe enough to cause his gut motility to slow down, he’s got a belly ache – it might be very mild and subtle, or it might appear as full-blown colic – but even the mildest colic pain can squelch his desire to eat. He must eat, but he won’t.

Meanwhile, he continues to pant in an attempt to blow off the heat that is killing him from the inside. But with each breath he can become more dehydrated, and the muscular activity involved in panting can actually stoke the fire, creating more heat.

As his cardiovascular system collapse, blood vessels to the muscles and skin begin to constrict. This keeps his too-hot blood close to his core, away from the body’s surface where it had the best chance of dissipating the extra heat. It also sets the horse up for myositis, because those muscles, which are sorely in need of nourishment after their workout, are suddenly being cut off.

Early in the course of heat exhasution, the horse might appear bright and normal, but he needs to be pushed to keep up the pace, and if you checked his rectal temperature it might be as high as 104° F. Horses that are stricken with heat exhaustion while performing some short-term, high-intensity exercise such as 3-day eventing or polo are likely to have less critical need for fluids and are simply in need of help of lowering their core temperature. For these horses, repeated cool (not cold) water baths and slow, relaxed walking in a light breeze is likely to do the trick. Getting the horse to eat and drink is rarely a challenge, so he’ll probably replenish his fluids and electrolytes on his own.

The endurance horse is a different case – his fluid and electrolyte debts are likely to be heavy and possibly life-threatening, and without the option of administering intravenous fluids and electrolytes, you’re severely limited. However, even though you’re in serious trouble in this situation and should move heaven and earth to get a competent equine veterinarian to come to your aid, you should still be able to help the horse if you’re prepared.

Prevention. Heat stroke can be prevented by limiting the horse’s exposure to predisposing situations and by insuring that hard-working and endurance horses drink frequently during prolonged exercise.

Heat Exhaustion Treatment

  1. CHECK VITALS Check the rectal temperature, the number of heart beats per minute, the number of breaths per minute, and listen to the abdomen for gut sounds and write all your findings. Re-check every half hour and record your progress. The normal temperature is 99-100.5°ree; F. The normal number of heart beats is 32-44 beats/min (adult). The normal respiratory rate is 8-15 breaths/min.
  2. ELECTROLYTES AND FLUIDS Gently but persistently get electrolytes and fluids into the horse orally. If he won’t eat or drink voluntarily, you’ll have to use some initiative to coax him.
  • Offer a bucket containing a half gallon of plain, cool (not cold) water and, right next to it, a second bucket containing a half gallon of electrolyte-treated water using a commercially prepared electrolyte powder designed specifically for endurance horses. Do not , under any circumstances, give this horse an electrolyte product made for calves or foals with scours (diarrhea) or for sprinting-activity performance horses&mdahs;the sodium bicarbonate in these products can make his heart unstable, and it can guarantee that he will be stricken with myositis on top of all his other problems.
  • If he shows no interest, rinse his mouth gently with a 20 cc syringe full of electrolyte-treated water, then offer the buckets again.
  • If he still shows no interest, you’ll have to force him. Remember, he’s still losing more water and electrolytes, probably a gallon or more per hour, even though he’s just standing there—they’re literally pouring out of him in his sweat and in his breath.
  • Start with the elctrolytes first. Read the instructions on the label of your elctrolyte product and calculate how much of the product would be required to prepare one quart of treated water. Mix the calculated amount with something yummy, then give him your concoction with the syringe. Still no luck? Then you need to be more aggressive. Give him one cup of water, by syringe, every five minutes, and give him another dose of elctrolyte mix, by syringe, every half hour. Do this for 2 hours, or until he begins drinking on his own.
  • If you don’t have an elctrolyte powder, you can make your own concoction with ingredients you can buy at any grocery store:

1 tablespoon regular table salt (sodium chloride) 1 tablespoon Morton’s salt substitue (potassium chrolide)
2 crushed tablets of extra-strength TUMSTM (calcium carbonate)
500 mg (2 crushed 250-mg tablets) of magnesium pills (magnesium oxide)
2 tablespoons Karo syrup or honey or molasses or pancake syrup
1 jar of baby food

  1. COOL HIM Meanwhile, be working on bringing his body temperature down by swabbing him every ten minutes with cool (not cold), dripping-wet cloths over his body, being sure to get him behind and between his ears, on his forehead, and on the underside of his neck, and in his armpits and groin. Do not run cold hose water over his back and rump—you could cause the blood vessels in those muscles to clamp closed even more than they already are, which will slow down his heat dissipation and threaten myositis.
  2. GIVE ASPIRIN As soon as you see signs of improvement: a bright look in the eye, heart rate beginning to drop to within normal range, respiratory panting beginning to resolve, body temperature coming back down to earth, and a return to voluntary eating and drinking, give a tiny dose of aspirin paste or gel orally to relieve residual muscle pain, encourage the still-spasming muscles to relax, and guard against the damaging effects of inflammation and toxicosis.
  3. MUSCLE TREATMENT If your horse is showing any signs of impending myositis (stiffening gait, tight or hard-feeling muscles over his back, croup, and loins, and/or coffee-colored urine), or if he has a history of tying-up in the past, he might benefit from a judicial dose of a medication that will help to dilate the constricted blood vessels in his major muscles. Again, if he is in a very tough shape, he might not be able to tolerate any medication smoothly. Rule of thumb: if he’s eating and drinking well on his own, and he seems to be showing general signs of recovery, he should be able to tolerate the medication.

 

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