Heat stroke can kill

Unfit horses with long coats are more prone to heat stress, writes Dr Mac.

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In hot South African summers both human and animal athletes can suffer from heat exhaustion. In horses, heat exhaustion is related more to the level of fitness and breed than to the daily temperature. Fit endurance horses, especially those with Arabian blood, are less likely to suffer from it than unfit horses of other breeds.

But in horses, heat exhaustion and heat stroke can kill. A related disease, the “thumps”, is an electrolyte imbalance due to overdosing endurance horses with incorrectly balanced electrolyte solutions, in the mistaken belief this improves performance. Experienced endurance riders know how to manage their horses, but the growing sport is attracting many amateur riders with less fit horses.

Even a 30km ride on an unfit horse, at speed in high summer, could cause heat stress. This can progress to heat exhaustion and even heat stroke. Even blanketed show horses transported long distances in poorly ventilated horse-boxes can suffer heat stress and heat exhaustion.

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Heat stroke can kill
The earliest symptom of heat stress is excessive sweating. In an unfit horse this can occur within 20 minutes of cantering or even trotting in hot weather. The heart rate goes to well over 60 beats per minute and the respiration rate increases. The horse starts “blowing”, or breathing hard with its nostrils extended and its sides heaving. Slow to a walk, soften your grip on the reins so it can extend its head and breathe more easily, and walk quietly until the respiration goes down.

You shouldn’t stop and dismount, as this often makes the muscles stiffen up. A gentle walk lets the blood circulate. Back at the stable, you can wash the horse off with cold water and lead it around gently until it’s dry. Giving a horse too much water to drink (more than a litre or two) before the horse has cooled down, can lead to colic. Instead, keep giving small amounts of water every few minutes and walk the horse again before giving more.

Heat exhaustion follows heat stress. The horse shows weakness and may stumble. Its respiration rate may even go higher than its heart rate as it pants with its sides heaving. The normal respiration rate for a horse is up to 18 breaths per minute, but may go as high as 70 per minute in heat exhaustion. The mucous membranes of the mouth are dry and pale and the eyes appear sunken. Often the horse is dehydrated and the skin can be pinched together.

The body temperature raises to 40ºC or above. In this case you need to get the horse cooled down as quickly as possible. Dismount and find a shady area, use a hosepipe or sponge the horse down with cool water (not ice water!) but keep it walking very slowly. Get it really wet and encourage evaporation using the wind or a fan, or even by waving sacks.

It can also drink cold water in small doses, 2â„“ at a time. If there was severe sweating it may have to take electrolytes orally. Don’t walk the horse a long way until it has completely recovered. Rather fetch it with a horse box. If heat exhaustion develops into heat stroke, the horse stops sweating, body temperature can rise to over 45ºC and the hair will look dry and spiky. The eyes are sunken and the horse doesn’t react to stimuli, but appears confused and may actually go down and start convulsing. This is a critical emergency and veterinary help is essential. Prevention is better than cure.

Give your horses a chance to get into the shade as much possible during endurance rides and shows. When transporting horses in hot weather, use a light sweat sheet and open the ventilation ports on horse boxes. On very hot days wet the sweat sheet so the wind blowing over the horse as you travel keeps it cool. Make sure your horse has enough salt in its normal ration and that drinking water is always available.

During a long-distance ride or at shows, stop now and then to let the horse drink. A sensible horse that isn’t deprived of water won’t drink too much. Use oral electrolytes carefully, during and after a ride or if the horse shows signs of heat exhaustion. Consult experienced endurance riders about electrolytes and only use solutions designed for endurance horses – cheaper ones designed for cattle, for example, cause problems.