Heat stroke in horses: causes, symptoms and treatment

Horses naturally regulate their body temperature through sweating and breathing. As sweat evaporates from the skin, it helps remove excess heat and keeps the body within a safe range.

Heat stroke develops when the body produces more heat than it can lose. As this happens, several changes occur:

• Sweating may become less effective or stop altogether
• Dehydration can quickly develop
• The heart and lungs are put under strain
• Internal organs may begin to fail
• The brain can be affected, leading to confusion or reduced awareness.

These changes can happen quickly, making early recognition and action essential.

Heat exhaustion and heat stroke sit on a spectrum of heat-related illness. Understanding the difference can help you respond quickly and appropriately.

Heat exhaustion is an earlier and serious stage, where your horse is struggling to cope with heat but may still be able to recover with prompt care. Signs often include heavy breathing, sweating, fatigue and a slower recovery after exercise.

Heat stroke is a much more severe condition and is always an emergency. At this stage, your horse’s temperature is dangerously high (often above 40.5°C), and the body’s natural cooling mechanisms have failed².

Heat-related illness can progress quickly and in some cases heat stroke may appear suddenly without clear warning signs.

High temperatures place extra strain on your horse’s cooling system. When humidity is also high, sweating becomes much less effective because sweat can’t evaporate as easily^1,2. This means heat builds up in the body more quickly.

Exercise naturally generates heat. During intense or prolonged work, particularly in warm weather, your horse may produce more heat than they can safely release. Without adequate breaks, cooling and hydration, this can lead to overheating.

Access to shade, fresh water and moving air helps your horse regulate their temperature, helping them to keep comfortable and healthy.

Transport can expose horses to enclosed spaces, limited airflow and stress. These conditions can make it much harder for them to stay cool, particularly during warm weather or long journeys¹.

In the early stages, signs may be subtle and include:

• Rapid or laboured breathing or panting
• Flared nostrils
• Raised temperature that doesn’t return to normal after rest
• Increased heart rate
• Excessive sweating, or in some cases reduced sweating
• Lethargy or reduced performance
• Muscle stiffness, spasms or weakness
• Reduced appetite or drinking
• Behavioural changes such as irritability, dullness or reduced awareness.

As the condition worsens, signs become more serious and indicate a medical emergency. These may include:

• Very high body temperature (typically above 40.5°C)
• Unsteadiness or lack of coordination
• Confusion or unusual, unpredictable behaviour
• Collapse or inability to stand
• Seizures
• Dark gums
• Signs of poor circulation, like a prolonged capillary refill time (taking more than two seconds for gum colour to return after pressing) or cold ears or limbs¹.

At this stage, immediate veterinary attention is essential to protect your horse’s life. 

If you suspect heat stroke, act straight away. Stop any activity and move your horse into a shaded, well-ventilated area. Contact your vet immediately and begin cooling measures without delay.

The aim is to reduce your horse’s body temperature as quickly as possible. Effective cooling methods include:

• Continuously apply cold water over the whole body without scraping water off. This helps reduce body temperature more effectively, as evaporation continues to draw heat away from the body^2,3.
• Increasing airflow using fans or natural ventilation.
• Offering water to drink.
• Monitoring temperature regularly to track improvement, if safe to do so.

Cooling should be continued until your horse’s temperature returns to a safer level.

Some common approaches can make the situation worse. It’s important to avoid:

• Delaying cooling while waiting for veterinary help
• Withholding water
• Covering your horse with towels or rugs as these will trap heat2
• Forcing your horse to move if they’re weak or unsteady
• Giving medication without veterinary advice.

Avoiding these mistakes helps make sure that cooling is as effective and safe as possible.

Providing clear information can help your vet respond quickly and effectively. Be ready to share:

• Your horse’s temperature, heart rate and breathing rate
• Recent exercise, work or travel history
• How long your horse has been exposed to the heat
• When the signs started and how they’ve progressed
• Any first aid or cooling measures already carried out.

This information supports quicker decision-making and helps your horse receive the best possible care.

Exercise and travel should be adjusted to reduce heat stress, such as working during cooler parts of the day, lowering intensity, providing more breaks and allowing time for your horse to acclimatise as temperatures rise⁴.

Access to fresh, clean water is essential, with intake monitored closely in warm conditions. Electrolytes may help replace salts lost through sweating, particularly for horses in work, as part of wider hot weather care.

Your horse’s environment should support effective cooling, including providing shade, good ventilation and avoiding overcrowded spaces. Regular monitoring is especially important during warmer periods, alongside good overall horse care in hot weather.

Some horses grow thicker, longer coats than others, like horses with Cushing's Disease, which can make it harder for them to cool down. You may need to clip the coat during the warmer months to help them stay cooler and safer.

1. Kang, H., et al. (2023) Heat stress in horses: a literature review. International Journal of Biometeorology, 67, pp. 957–973. 
2. Darby, S. (2025) First Aid for Horse Owners. EDIS. 2025(5).
3. Marlin, D. (2025) Cooling people, dogs and horses – cooling facts and cooling myths. AskAnimalweb.
4. Marlin, D., et al. (2018) Optimising performance in a challenging climate FEI Sports Forum.