The days are hot. You’re sweating and it’s too miserable to go outside. You go to the stable in the evening to visit your horse. You have an automatic waterer. But you’re concerned for your horse. How do you know if your horse is dehydrated?
◆︎ Reliable signs of dehydration:
➡ Skin pinch. Pinch the skin on the neck. It should return to normal after 1-2 seconds. If it takes longer, it could be a sign of dehydration. If it takes 4-6 seconds, it could indicate severe dehydration. Caveat: Older horses may take longer due to loss of elasticity in the skin. Proactively, do a pinch test when the horse is not at risk for dehydration, so that you will know what “normal” looks like for your horse.
➡ Capillary refill time: Press your thumb against the gum under the lip for 2-3 seconds, then release. When you release your thumb, the skin should be blanched and have turned a whitish color. Count the number of seconds that it takes for the gums to return to pink. If it’s longer that 1-2 seconds, your horse may be dehydrated.
➡ Dry, tacky gums: Horses usually have plenty of moisture in their mouth. If the gums and mucus membranes of the mouth feel tacky and on the dry side, it could be a sign of dehydration.
◆︎ Unreliable signs of dehydration:
☛ Sweat: Seeing the amount of sweat on a horse is not a reliable sign of dehydration. In dry climates, the sweat could evaporate readily. This could lead you to a false sense of complacency that your horse didn’t sweat very much.
☛ Refusing water: Horses that become extremely dehydrated may not become thirsty. Loss of electrolytes can suppress the thirst mechanism. Without the thirst mechanism activated, the horse doesn’t feel like drinking. Additionally, if the water is hot, is dirty, has bird droppings in it, or is otherwise unpalatable, the horse may refuse water, but still be thirsty.
☛ Lethargy: While horses that are dehydrated can become lethargic, this could also be due to oppressive heat and humidity. This is not a reliable sign of dehydration.
☛ Reduced appetite: Excessive heat can cause a suppression of appetite, independently from dehydration.
☛ Flared nostrils: Flared nostrils in the summer is a sign of overheating, but is not necessarily associated with dehydration. Flared nostrils when hot is frequently a sign of insufficient sweating, which could also be a sign of anhidrosis.
☛ Tying up: While horses may tie up during dehydration, this can happen due to overexertion, electrolyte imbalance, or genetic predisposition.
☛ Colic: Dehydration can cause impaction colic. However, dietary factors can play a significant role.
◆︎ How fast can dehydration happen?
Horses can become dehydrated within a few hours of not drinking enough. For instance, if the waterer to the horse’s paddock is broken and there are elevated temperatures, the horse could rapidly become dehydrated. This can be exacerbated when the horses are fed hay or are on dry lot. In those instances, the horse’s water intake is reduced because they are not eating grass, which is about 90% water. A broken waterer in the paddock could be catastrophic within a day or two.
◆︎ How to reduce the risk of dehydration:
➡ Be sure that plenty of cool, fresh water is available.
➡ Add salt and/or electrolytes to the horse’s bucket.
➡ Offer clean, free-choice salt or electrolytes separately from the horse’s feed.
➡ Consider adding water to your horse’s feed bucket to increase the amount of fluid intake.
➡ Wet hay at feed time to increase moisture content. Be careful that it doesn’t spoil in the heat of the day.
◆︎ Severe dehydration:
Severe dehydration can be life-threatening and should be considered a medical emergency. Your veterinarian has the ability to administer intravenous fluids to help rehydrate your horse.
◆︎ Take home message:
The old saying of “an ounce of prevention is worth a pound of cure” is certainly true for dehydration. The best way to prevent it is to have plenty of clean, fresh water available for your horse. Increased salt or electrolytes can trigger your horse’s thirst mechanism.
We do the best that we can do for our horses. Understanding dehydration is a part of that.
Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay, MSc. 2025