Why is water essential for horses?

Water is a fundamental nutrient, essential for the proper functioning of the horse’s body. It is crucial for the digestive system, metabolism, and thermoregulation. It is responsible for the transport of nutrients, removal of toxins, and proper digestion and absorption of feed. Horses lose water through respiration, sweating, urination, and defecation; therefore, constant access to water is essential to maintain the animal’s health and condition.

Water content in the horse’s body
The total water content in the body of an adult horse amounts to 61–72% of body weight, and in foals it can be as high as 84%. Water is present in cells, the extracellular space, and the gastrointestinal tract, where it serves as a reservoir during periods of limited access to fluids. Horses fed hay store more water in the intestines than those on a complete feed diet, which affects their overall water balance.

Daily water requirement
The average daily water intake of a horse at rest is approximately 50 ml per kilogram of body weight (range 41–67 ml/kg). The amount of water consumed is influenced by diet—horses consume more fluids on a hay-based diet (water-to-feed ratio of 3.2–4.4) than on a grain-rich diet (ratio of 2–2.6). Lactating mares have an increased water requirement of 75–100 ml/kg of body weight, which may be even higher at elevated temperatures.

Water loss in horses
Horses lose water mainly through:

Urine – they excrete 6–29 ml of urine per kg of body weight daily.
Feces – the primary route of water loss, especially in hay-fed horses.
Sweating – a key thermoregulatory mechanism that significantly increases water requirements.
Respiration – water is also lost through exhaled air.

Intestinal diseases such as diarrhea can increase fluid loss—affected horses may excrete up to 61.8 liters of water per day, compared with only 25.8 liters in healthy horses.

Dehydration in horses – symptoms and consequences
Dehydration leads to reduced performance, digestive problems, and serious conditions such as colic. Symptoms of dehydration in horses include:

Dry skin and mucous membranes,
Apathy and weakness,
Reduced urine output,
Increased heart rate and respiration.

Prolonged dehydration may result in thickening of intestinal contents, which increases the risk of colic and metabolic disorders. Proper hydration is particularly important for sport and working horses.

Electrolytes and hydration in horses
Electrolytes such as sodium, potassium, chloride, calcium, and magnesium play a key role in maintaining water–electrolyte balance. Horses lose large amounts of electrolytes through sweat; therefore, supplementation is essential, especially during hot weather, physical exertion, and transport. Electrolytes can be provided in feed, water, or as specialized preparations. However, it should be remembered that excessive electrolyte intake without adequate water supply may lead to health problems.

How to ensure an adequate amount of water for a horse?
Constant access to clean water – horses should have access to fresh water at all times.
Adjusting water supply to the diet – horses on hay-rich diets require larger amounts of fluids.
Monitoring hydration status – skin elasticity tests and observation of mucous membranes can help detect early signs of dehydration.
Electrolyte supplementation – particularly important for sport horses and during hot weather.
Appropriate drinker height for foals – should be 75–90 cm.

Summary
Water is a key element of a horse’s diet, influencing its health, condition, and performance. Water deficiency can lead to serious health problems; therefore, water intake should be continuously monitored and adjusted to the individual needs of the horse. Ensuring proper hydration, electrolyte supplementation, and an appropriate water source is the foundation of a healthy diet and good animal welfare.

References
Freeman DE. Effect of Feed Intake on Water Consumption in Horses: Relevance to Maintenance Fluid Therapy. Front Vet Sci. 2021 Mar 1;8:626081. doi: 10.3389/fvets.2021.626081. PMID: 33732739; PMCID: PMC7956953.
Geor, Raymond J., et al., editors. Equine Applied and Clinical Nutrition: Health, Welfare and Performance. Elsevier, 2013.
Meyer, C., & Coene, E. (2001). Horse Nutrition (transl. M. Miękisz). Warsaw: PWRiL.
Lindinger MI. Oral Electrolyte and Water Supplementation in Horses. Vet Sci. 2022 Nov 10;9(11):626. doi: 10.3390/vetsci9110626. PMID: 36356103; PMCID: PMC9696292.