Heat stress in horses

As summer approaches, rising temperatures and humidity can place significant strain on horses, particularly those in regular work or competition. Without appropriate management, hot weather can negatively impact both health and performance, increasing the risk of heat stress.

Horses are especially vulnerable during summer due to factors such as high ambient temperatures, humidity, poor airflow, dehydration, inadequate ventilation, and prolonged exposure to direct sunlight. When combined with exercise or transport, these conditions can quickly overwhelm a horse’s ability to regulate body temperature.

How horses regulate heat

During exercise, a horse’s muscles convert energy into movement, with excess energy released as heat. To prevent overheating, horses rely on several key cooling mechanisms:

• Sweating, which allows heat to evaporate from the skin
• Increased blood flow to the skin, helping transfer heat away from vital organs
• An increased respiratory rate, aiding heat dissipation

In hot or humid conditions, however, these natural cooling processes may become less effective. When a horse cannot adequately disperse excess heat, body temperature can rise to dangerous levels, leading to heat stress or, in severe cases, heat stroke.

Signs of heat stress in horses

Heat stress can develop during or after exercise and may worsen rapidly if not addressed.

Common warning signs include:

• Excessive sweating
• Little or no sweating (a possible sign of anhidrosis)
• Rapid or laboured breathing at rest – generally over 20 breaths per minute
• Persistently elevated heart rate that does not recover with rest
• Hot or dry skin
• Elevated rectal temperature (generally above 39°C)
• Lethargy, weakness, or reduced coordination

Any combination of these signs warrants immediate attention.

How to tell if a horse is sweating (or not):

Sweating is one of the main ways horses cool themselves, but it can be difficult to detect – particularly in dark-coloured or thick-coated horses. Some horses may suffer from anhidrosis, a condition where sweating is reduced or absent, increasing the risk of overheating. To assess sweating:

• Check common sweat areas such as the neck and shoulders, chest, between the front legs, and under the saddle.
• Run your hand through the coat – a sweating horse will feel damp and cooler to the touch.

Reducing the effects of heat stress

If you suspect your horse is experiencing heat stress, act immediately. Immediate steps include:

• Move the horse into a cool, shaded area.
• Begin active cooling using cold water, focusing on the neck, chest, and inside the legs where blood vessels are close to the skin.
• Allow the horse to rest quietly.
• Ensure fresh, clean water is always available.
• Electrolytes may be offered in addition to plain water, but horses shouldn’t be forced to drink electrolyte solutions.

If symptoms persist, worsen, or if the horse’s temperature remains elevated, seek veterinary assistance immediately. A veterinarian can assess severity, provide treatment, and advise on recovery protocols.

Ongoing monitoring and recovery

Horses that have suffered significant heat stress may be more susceptible to overheating in the future. It’s important to monitor them closely in the days and weeks following a heat event and to reintroduce work gradually. A veterinary check is strongly recommended before returning to full exercise.

Preventative strategies such as adjusting exercise times, improving airflow, ensuring adequate hydration, and providing shade can significantly reduce the risk of heat stress during the warmer months.

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