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Dehydration in Horses


dehydration in horses

Dehydration is serious and potentially life-threatening. It can occur all year round, and spotting the early signs of dehydration can be difficult. The initial symptoms of dehydration can be subtle, meaning it may be missed. Furthermore, dehydration can cause potentially serious secondary issues.

Preventing dehydration - and being able to identify and act on it early - is key. This blog covers the causes, symptoms, dangers and prevention of dehydration in horses. 


Causes of Dehydration in Horses

Dehydration in horses is generally caused by one or more of the following:

Excessive sweating: Like humans, horses sweat to help regulate their body temperature. This causes fluid loss, which can contribute to dehydration. Strenuous exercise and high temperatures can cause horses to sweat more than usual. Excessive or unusual sweating can also be a sign that a horse is unwell.

Diet: A large proportion of a horse’s water intake comes from eating. Hay has a much lower water content (15%) than haylage (30-50%) or grass (80%). Therefore, stabled horses or those that are fed mostly on hay can be more vulnerable to dehydration. Horses on box rest or those that are prone to laminitis are also likely to consume more hay and less grass.

Failure to drink: Stress or illness can make a horse less likely to drink. Lack of access to fresh, clean water can also become an issue without the owner realising - for example, due to a leak in an automatic drinking system. Depending on the herd dynamics, resource guarding may prevent an individual from accessing enough water from a communal drinking trough whilst turned out.


Symptoms of Dehydration in Horses

The early symptoms of dehydration can be subtle and may be missed. Therefore, it is important to pay attention to your horse, especially during or after strenuous exercise. Horses may be more prone to dehydration at competitions or on hot days, but dehydration can occur at any time of year and is not always associated with exercise. The symptoms of dehydration in horses include the following:

  • Poor performance - possibly due to fatigue or tiredness
  • Depression (disinterest in surroundings)
  • Lethargy (tiredness, lack of concentration or energy)
  • Darker coloured urine
  • Dullness in the eyes
  • Dry skin and / or mouth
  • Thick, sticky saliva
  • Not passing urine for an extended period of time 


There are a couple of ways that you can test to check if your horse may be dehydrated:

The skin pinch test: Pinch a fold of skin (usually over the neck) and see how long it takes to return to normal.  If this takes longer than a couple of seconds, then the horse may be dehydrated.

The gums / capillary test: If your horse’s gums are moist to touch, then the horse is probably well hydrated. Tacky or dry gums indicate dehydration. The capillary test involves pressing the gum to see how quickly the white indentation returns to pink. If this takes longer than 2 seconds, then the horse is probably dehydrated or unwell.

Dehydration that occurs frequently, in the absence of an obvious cause (e.g. hot weather or strenuous exercise) or in conjunction with other symptoms may indicate that the horse is unwell and you may need to contact your vet. Furthermore, some of the symptoms listed above may be caused by issues other than dehydration. 


Why is Dehydration so Dangerous?

Dehydration can be prevented and mild dehydration can be rectified without causing any long-term harm to the horse. However, dehydration in horses can cause secondary, serious health problems if it is not spotted and dealt with properly. 

Water is essential for a range of bodily functions. For example, it aids digestion, transports nutrients around the body, aids thermoregulation and assists various metabolic processes. Dehydration can interrupt these processes, which can cause more serious problems. 

Impaction colic is one of the more serious conditions that can be caused by dehydration. Common in the winter months, partially digested food matter can build up in the gut, causing an obstruction. Colic can cause long-term damage to the horse’s digestive system and in serious cases it can be fatal.

Horses won’t always drink, even if they are dehydrated. Some horses are fussy drinkers and may refuse water straight from the tap or when away from the yard. This may cause owners to assume their horse doesn’t need a drink, when actually, they still require fluids. Therefore, it’s important to have an alternative source of water available - as a mash, for example. 


How to Prevent Dehydration in Horses

  • Always supply fresh, clean water
  • Ensure there is enough water (and water troughs / buckets) for all horses and keep an eye out for resource guarding when turned out
  • Feed electrolytes, especially for horses in work in the hotter months
  • Walk the horse off in the shade after exercise to help them cool down and reduce sweating
  • Cool the horse with water to bring the body temperature down and reduce sweating
  • Provide shade
  • Feed a mash and consider haylage or grass* over hay

*Special care should be taken with overweight horses, good doers or horses prone to laminitis. In these cases, higher grass intake may not be appropriate.



Dehydration is not just about a lack of water. Electrolytes are essential to the body being able to process and retain water. A loss of electrolytes makes dehydration worse, and these need to be replaced along with the water. 

Electrolytes are minerals found in fluids, which aid neuro-muscular function and allow the body to retain water. A lack of electrolytes can cause tiredness, affect performance and contribute to dehydration. Electrolytes are lost through sweating, and they are usually added to water to help the horse rehydrate after exercise.


What to do if Your Horse Becomes Dehydrated

  • Encourage drinking - offer the horse clean, fresh water
  • Give the horse a soaked feed or mash to encourage water intake, especially if he or she refuses water
  • Provide electrolytes - these can be added to water to create an isotonic solution. Electrolytes can also be given in food or as a paste. A large single dose of electrolytes can worsen dehydration in the short term as it causes the body to absorb more water from the blood vessels, so they are best given little and often.


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