Thumps. Thumps (synchronous diaphragmatic flutter) refers to a warning sign of underlying metabolic problems. It's detectable as muscle twitches in your horse's flank. If your horse suffers dehydration and electrolyte losses in the sweat, he may lose sufficient amounts of calcium, potassium, and magnesium ions in his bloodstream. When this happens, his phrenic nerve (which runs across his heart to supply nerve function to the diaphragm muscles) becomes more reactive, firing in synchrony with each heartbeat. This causes his diaphragm muscles to contract and "flutter."
Sign of thumps: Sometimes, you'll see no more than a flutter of the flank muscles as the diaphragm contracts. Or, you might feel a twitch in the flank area. Note that a horse may only thump on one side, and/or the thumping may occur intermittently. If you ignore this condition, and your horse continues to deteriorate with dehydration and electrolyte imbalances in the face of continued exercise, he could suffer myositis, colic, laminitis, heat exhaustion, and/or collapse.
What you should do: If you spot any signs of thumps, dismount, and offer your horse feed and water. Keep your horse still. In many cases, rest, rehydration, and electrolyte restoration will resolve the problem. If symptoms persist, call your veterinarian.
Consider ice water. If you trail ride in a humid climate, you can cool your horse with ice water. Research from the 1996 Olympics in Atlanta, Georgia, shows that in hot, humid climates, you can apply ice water with little risk of muscle cramping, because humidity slows the cooling process. In more arid climates, however, ice water may cool your horse's large muscle groups too quickly, resulting in myositis or "tying up." (See "Heat-Related Conditions" on page 81.) To make sure he's cooling down properly, check his rectal temperature; once his chest is cool to the touch, you can stop applying ice water.
Offer water. Offer a bucket of water to your horse following exercise. If you've been riding him at a fast gait, offer him small, frequent drinks until he's cooled down a bit. But if you've been riding him at a slower, steady pace for a long period, encourage him to drink as much as he'd like.
Find shade. Lead your horse to a shady area, preferably where there's good air circulation, such as a breeze. An enclosed space with stagnant air adds to heat retention.
Turn on a fan. Place a fan in your barn, and aim it on your horse in hot weather. As air flows across his body, it'll help pull heat off his skin. As an added bonus, the fan's breeze will help keep insects from pestering him.
Call your veterinarian. If your hot horse doesn't cool down within 10 minutes, or his condition worsens, call your vet immediately. Heat stress can endanger your horse's life. Your vet will likely give your horse intravenous fluids to treat dehydration and shock, and to cool organs and muscles.
Keep Your Cool
To help your horse stay cool and out of danger of heat stress, you'll need to keep cool so that your thinking remains clear and you can take action in an emergency. Your ride will also be more enjoyable. Follow these tips to keep cool on the trail.
Wear breathable clothing. Wear breathable clothing, such as cotton or manmade materials designed for hot-weather wear. (Non-breathable clothing will keep in your body heat.) Also look for clothing that blocks ultraviolet rays to help avoid sunburn.
Drink plenty of water. Maintain your own hydration, drinking water frequently.
Consider electrolytes. Maintain your own electrolyte balance with sports drinks.
Eat for the heat. Maintain your energy level by eating power bars, fruit, and carbohydrates.
Cool off. Buy a neckerchief with cooling gels. On the trail, wet the neckerchief with your drinking water or in a stream to activate the gels, and tie it around your neck. Also, soak your head before putting on your helmet and while on the trail. Take frequent breaks in the shade.
