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Dehydration can be detrimental to human and equine performance alike. A sound knowledge of feeding in hot and challenging conditions can give ordinary riders a competitive edge during the British summer’s hot spells.

In general, all horses competing in hot weather require a greater level of fat in their concentrate rations to provide energy. Some horses may also have specific nutritional requirements to help manage existing or potential problems such as azoturia, where a low-starch, high-fibre and oil diet is advised.

Replacing some of the starch in the horse’s diet with oil (fat) also helps to diminish heat production during work by reducing microbial fermentation in the hindgut, which is extremely beneficial in hot climates. “Fat also provides slow-release energy, so helps sustain stamina and reduce excitability,” explains nutritionist Lizzie Drury.

It is also important to maintain a suitable amount of forage in the diet.

“Forage will help to maintain the health of the digestive tract and acts as a reservoir in the hindgut, trapping vital water and body salts,” says Lizzie. “Too much concentrate can provide excess starch in the diet, which may make the horse too fizzy and disturb the delicate microfloral balance.”

The harder the horse works, the more vitamins and minerals it will need. The stress of intense exercise on bones may also slightly increase the requirements for minerals involved in bone integrity, such as calcium, zinc, magnesium, phosphorous and copper.

“Commercially available feeds, which are formulated specifically for performance, would take these factors into account, so that the only extra ingredient needing to be added would be correct electrolyte supplementation to combat the effects of sweating,” Lizzie adds.

Sweating is the body’s natural cooling system and allows a horse to cool itself during and after exercise. It is a sure sign that the horse is losing fluids and therefore electrolytes.

“Within those fluids electrolytes are escaping from the body at alarming rates,” explains Lizzie. “These body salts control the fluid balance of the body by regulating movement of water in and out of the cells and changing the concentration of the contents. They are responsible for an extraordinary array of critical body processes: muscle contraction, the pumping of the heart and the moving of food through the digestive tract, to name a few.”

The amount of sweat and electrolytes lost, and the measure of electrolyte supplementation required, depends on several factors. Dr Joe Pagan, president of Kentucky Equine Research in America, looked at sweat loss in horses at the 1996 Atlanta Olympics. By measuring the horses’ body weight before and after the speed and endurance phase of the three-day event, he found that, on average, horses lost 18.4kg of body weight – about 15 litres of sweat.

The thirst response is nature’s way of preventing horses from becoming dehydrated, and it is thought that the urge to drink depends on having sufficient sodium concentrations in the blood.

When the horse sweats lightly, he loses water but the amount of electrolytes lost is minimal. The body recognises this water loss and seeks to make up the deficit by making the horse thirsty.

However, if the horse is sweating heavily and for a prolonged period of time he will lose significant amounts of water and electrolytes, so the level of sodium in the blood does not rise a great deal. This means the horse is not stimulated to drink, even though he is dehydrated.

Furthermore, when horses sweat profusely they are unable to drink quickly and frequently enough to replace the lost fluids. This can lead to fatigue and muscle weakness.

Top tips for hot weather

  • Don’t take unnecessary risks or push your horse too hard in very hot weather – and take it easy if you are competing. Heat exhaustion is no fun for horse or rider
  • Reduce your speed if undertaking fast work and concentrate on other areas, such as accuracy and obedience
  • Monitor your horse’s temperature, pulse and heart rate in order to avoid heat stress
  • Allow sufficient ‘cool down’ periods in walk when competing to allow the body’s internal cooling mechanism to function
  • Warm up in the shade or indoors where possible and try to wait in shade rather than in direct sunlight
  • Avoid the hottest part of the day when training
  • Allow the horse free access to water before and after exercise
  • Cool the horse off after competition with cold water, leaving it on the skin for a few seconds, before scraping off the excess and repeating
  • Once the horse has cooled down, hydrate yourself, too. Aim to drink one to two litres of water a day and keep a full water bottle to hand.
  • Add 20-40g of salt daily to the feed of horses in light work, increasing this amount with the horse’s workload
  • If the horse is sweating for prolonged periods on a daily basis provide an electrolyte supplement, following the manufacturers’ instructions
  • Read the full feature on the role nutrition can play in helping horses cope with competing in hot weather in the August issue of HORSE magazine, on sale now

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