Dehydration is a serious problem in competing and working horses, especially during hot weather. Horses are very sweaty animals and can quickly become dehydrated.

Horses competing in endurance racing or engaging in sustained heavy exercise are at the highest risk of dehydration.

Dehydration occurs when your horse loses excessive fluids from sweat, urine, feces, and respiration. If your horse does not drink enough to offset the fluid loss, she can become dehydrated.

The most common signs of dehydration are poor performance, loss of skin elasticity, weakness and increased respiratory rate. Dehydration also increases the risk of heat stroke, tying-up and slow exercise recovery.

Knowing the signs of dehydration and how to help keep your horse hydrated is important for every horse owner.

Dehydration in Horses

Horses become dehydrated when fluid loss is not offset by adequate water consumption. Water is one of the most important nutrients for the horse and makes up 61 – 72% of a mature horse’s body weight.

To maintain appropriate hydration status, the average non-working horse must drink at least 6.6 gallons (25 litres) of water daily. [1]

If your horse is exercising or in a hot climate, the amount of water they need to drink increases. [1]

Exercising horses can lose +10 litres of moisture per hour through sweating. Even in moderate environmental conditions, dehydration can occur after 3 hours of exercise. [3]

Field studies of endurance horses show that fluid losses are greatest by mid-ride. Horses can lose 20-25 litres total after an 80-kilometre ride. [4]

During heavy, prolonged exercise on a hot day, a horse’s water needs can increase by 300%. [2] Offer your horse water multiple times during long, intense workouts or when a horse is being exercised during hot weather.

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Illness or fever can also cause dehydration if a horse isn’t drinking sufficiently.

Additionally, horses with severe and acute gastrointestinal infection are at risk for dehydration. Severe diarrhea caused by colitis or copious gastric reflux caused by enteritis can result in life-threatening fluid losses.

A horse with chronic loose manure can have four times greater fecal output than a healthy horse. To compensate for increased fluid losses, they would need to double water intake. [1]

Electrolyte Imbalance

Sweating also causes the loss of electrolytes including sodium, potassium, and chloride. [14]

These electrolyte minerals are needed to maintain proper fluid balance, nerve and muscle function, as well as acid/base balance in the horse’s body.

Low electrolyte levels can actually suppress your horse’s thirst response and worsen dehydration, especially with continued exercise and sweat loss. [17]

Feed your horse 1-2 tablespoons of salt every day to promote water intake, and use an electrolyte supplement in hot weather or after heavy work.

Top 10 Signs of Dehydration in Horses

Every person who cares for or owns a horse should be able to recognize the early warning signs of dehydration.

Early detection can help you ensure you can rehydrate your horse quickly and avoid heat stroke or other complications.

1) Loss of Skin Elasticity

The skin pinch test can show loss of skin elasticity. Though not completely foolproof, it is one of the most common ways to check for dehydration in horses.

To perform this test, use your thumb and forefinger to gently pinch the skin of your horse’s neck, just above the point of the shoulder.

In normal circumstances, the skin should snap back quickly (1-2 seconds), but dehydrated skin will form a wrinkle or tent and take longer to disappear.

Older horses may have a longer-lasting skin compared to younger horses. The anatomical position of the skin pinch test as well as coat moisture can also affect the duration of tenting.

To gauge results, it’s important to know what is normal for your horse. Practice the pinch test several times on different days to set a baseline for your horse. [5]

2) Slow Capillary Refill Time

Dehydration can also be determined through the gums and capillary refill time (CRT). Lift your horse’s upper lip, and press your thumb on the upper gum for one to two seconds to blanch the surface.

A well-hydrated horse will have pink and moist gums. The colour should return in less than 2 seconds after you press your thumb into the gum.

A dehydrated horse will have dry or tacky mucous membranes. Additionally, their CRT will be prolonged, meaning it takes longer than 2 seconds for color to return to the blanched area. [6]

A failure for colour to return quickly in the gums can also mean that your horse is going into shock. Call your veterinarian right away if this occurs.

3) Rapid Changes in Body Weight

Changes in body weight can also be used to determine fluid balance during exercise. Dehydration is commonly described based on the percentage of body weight lost. [4]

Body weight is typically monitored in endurance races as well as in pulling competitions. If horses lose too much body weight, she can be eliminated from the competition.

Dehydration greater than 15% can be fatal. This would be equivalent to a weight loss of 95 kg for a 500 kg horse. [1]

4) Weariness or Weakness

A horse that is visibly lethargic, tired, or weak may also be dehydrated. It is best to allow a tired horse to rest and offer water and electrolytes.

Other illnesses or issues can also cause weariness and/or weakness. Monitor your horse to determine whether veterinary attention is required.

5) Stiffness

Horses that are stiff during stretching or exercise may also be dehydrated. If you regularly stretch your horse and know how flexible she is, changes in flexibility can indicate dehydration.

6) Dark Urine

A dehydrated horse may either not urinate often or produce urine that is dark (brownish) and more pungent than normal.

7) High Resting Heart Rate

For most adult horses, a normal resting heart rate is 25 to 40 beats per minute. A heart rate above 60 beats per minute could indicate dehydration.

8) Increased Respiratory Rate

An increased respiratory rate that does not return to normal during a cool-down routine is another sign that your horse may be experiencing heat stress and dehydration.

9) Tying Up

Though some horses are prone to tying up due to metabolic conditions such as Recurrent Exertional Rhabdomyolsis or PSSM, other horses may only experience tying up after strenuous exercise when dehydration is present.

Signs of tying up include:

  • Sweating
  • Stiffness
  • Reluctance to move
  • Dark-colored urine
  • Muscle twitching in the flank region

10) Altered Blood Work

Certain blood tests can also reveal dehydration in your horse. Examples of laboratory tests that can indicate dehydration include packed cell volume (PCV), serum total protein (TP) and osmolality in peripheral venous blood. [3]

Assessing the Level of Dehydration

Horses often show several of the above signs when they are dehydrated. The following table shows the level of dehydration associated with results on tests of skin tenting and capillary refill time (CRT): [7]

Dehydration Skin Tent CRT Other Signs
5-7% 2-3s >2s Mucous membranes may be normal
8-10% 6-10s >2-4s Dry/tacky mucous membranes
Possible signs of early shock
10%-12% Remains tented >5s Cold extremities
Other signs of shock
12-15% Shock, death


Signs of shock from severe dehydration include:

  • Irregular heartbeat
  • Weak pulse
  • Poor jugular refill
  • Cold extremities
  • Weakness, incoordination