The dangers of thermal stress

As British riders across the Olympic disciplines prepare for Athens, the scorching summer heat of Greece will be an additional challenge for horse and rider alike. Nutritionist Lizzie Drury believes it is vital we understand the effects of the dry heat expected at the Games for the welfare of all concerned.

“Athens is generally hot and dry with temperatures reaching 40 degrees celcius in July and August. The Olympic horses will face various physical challenges caused by the heat,” she says.

Extensive research has been carried out on exercising horses in extreme heat since the Stockholm World Equestrian Games in 1990, and it has been concluded that horses working in these conditions will experience increased thermal stress.

“This occurs when the horse’s body temperature increases, usually exceeding 105ºF (40.5ºC), and the horse starts to loose fluids, including electrolytes, through sweating,” explains Lizzie.

“If the rider does not act on these indicators of thermal stress and compensate for them, the horse is likely to suffer from fatigue or ER (exertional rhabdomyolysis or azoturia) – or may even collapse.”

Usually, thermal stress develops from over-exertion leading to overheating, or if weather conditions have taxed a horse’s ability to dissipate heat or interfered with fluid and electrolyte balance.

“You can reduce thermal stress by ensuring that your horse is properly conditioned, building muscle in place of fat,” says Lizzie. “This also develops capillary beds, improving oxygen circulation in the tissues and flushing heat to the skin surface.

“During competition, the simplest approach to combat thermally stressful conditions is to adjust the time of exercise and/or competition to avoid such conditions, such as competing in the early morning. This is preferable to early evening when the air temperatures often remain high due to heat stored in the ground.”

The extent to which horses suffer from thermal stress also depends on factors other than the temperature, including the type and speed of work the horse is being asked to do and the terrain he may have to cover. Some of these less-obvious factors include:

• Breed – for example, some Thoroughbreds and Arabs have a metabolic defect of calcium regulation and muscle contraction
• Body composition
• Length of coat
• Management and acclimatisation
• Body fat – Horses carrying greater amounts of fat are more likely to suffer the effects of extreme heat than lean horses as fat acts as an insulator, preventing excess heat from escaping through the skin

Although some of the show jumping at the Olympics is scheduled in the morning, most will take place in the afternoon and evening, which is not ideal, given the problems of thermal stress.

Various factors, such as TV broadcast limitations, influence the Olympic organisers’ schedule – but riders can only hope that the temperatures will have cooled down by the time the horses compete.

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