Dehydration in horses: causes, signs and treatment

Early signs are often mild and best identified through changes in routine. These may include:

• Reduced or darker urine
• Drier or fewer droppings
• Mild lethargy
• Changes in drinking behaviour, such as drinking more or less than usual, which can be an important sign your horse's fluid levels are changing

As dehydration progresses, signs become more noticeable and may include:

• Increased heart rate
• Dry mouth and thick saliva
• Dull or sunken eyes
• Gums that take longer than normal to return to their usual pink colour after being gently pressed with a finger (known as capillary refill)
• Gums appearing darker or red instead of a healthy pink

The presence of several signs together increases the likelihood of dehydration.

Hot weather conditions and exercise increase sweating, which leads to the loss of fluid and electrolytes. Without replacing these losses, your horse's normal body functions can be affected and recovery after exercise may be slower².

Limited or reduced water intake is one of the most significant causes of dehydration. Horses without access to water can lose a substantial proportion of body weight and develop clear signs of dehydration³.

Illness can contribute to dehydration by increasing fluid loss or reducing your horse's desire to drink. Conditions such as diarrhoea or fever can quickly upset fluid balance, even when outward signs appear mild.

Transport is a common risk factor for dehydration due to a combination of reduced drinking, stress and environmental conditions. Some horses can find transport stressful, particularly if they aren't offered water³.

Additional contributing factors include:

• Long journey duration
• Exposure to heat or direct sunlight
• Fatigue and limited opportunities to drink

Providing constant access to clean, fresh and palatable water is essential. Monitoring how much your horse drinks is equally important, particularly during higher-risk situations such as heat, work or travel.

Key points to consider:

• When travelling long distances, plan rest breaks every three to four hours and offer water⁴.
• Horses may drink less in unfamiliar or in environments they might find stressful¹.
• Drinking behaviour is a reliable sign of hydration².
• Water intake should be actively monitored, not assumed.
• Soaking feed can provide extra water, but it shouldn't be relied upon as the main way to keep your horse hydrated⁵. Fresh drinking water should always be available.

Electrolytes play an important role in maintaining hydration⁶:

• Replacing electrolytes alongside water improves rehydration
• Electrolytes may be beneficial before strenuous exercise, competitions or longer periods of travel where significant sweating is expected
• Solutions must be correctly balanced and not too concentrated
• Palatability is essential so horses will willingly drink.

Follow the manufacturer's instructions and make sure fresh water is always available when electrolytes are used.

Good housing and field management can help reduce the risk of dehydration. Consider:

• Providing multiple water sources, particularly for horses kept in groups
• Regularly checking water troughs and buckets are clean and working correctly
• Monitoring horses that may be prevented from drinking due to resource guarding
• Providing access to shade during hot weather.

If you suspect your horse may be dehydrated, offer fresh water and monitor them closely. If signs persist, worsen or you're concerned about their condition, contact your vet for advice.

Rehydration focuses on replacing both fluids and electrolytes. This can be achieved by providing fresh water and appropriately diluted electrolyte solutions where suitable. Fluids and electrolytes are absorbed through the digestive system and help restore normal hydration.

The digestive system can act as a temporary reservoir, allowing fluids and electrolytes to be absorbed efficiently when needed⁶.

Some approaches can be misleading or ineffective, including:

• Solely relying on a single test, such as pinching the skin on the neck and seeing how quickly it returns to normal shape (sometimes called the skin pinch test), or checking gum dryness²
• Assuming hydration without monitoring intake
• Using overly concentrated electrolyte solutions⁶
• Relying on soaked feed alone to improve hydration⁵.

Avoiding these mistakes helps make sure hydration is assessed and managed more accurately.