The most important nutrient in the horse’s diet is one often forgot about: water.

An adult horse’s body is composed of roughly 70% water, which equates to about 360 litres of water for the average 500-kg horse. Foals have an even higher water content, roughly 80%. The amount of water required daily by horses is determined by the amount of water losses from its body. These losses occur through faeces, urine, sweat, etc. An individual horse’s water requirement is dependent on the age, environment, temperature, humidity, fitness level, and type/quality of feed consumed. In the case of the lactating mare, stage of lactation also plays a large role in water requirement.

Average water intake for a 500-kg horse

• Mature, idle, 20° C: 21-29 litres
• Mature, idle, 30° C: 42-54 litres
• Lactating mare: 40-63 litres
• Moderate exercise, 20° C: 26-46 litres
• Moderate exercise, 30° C: 72-92 litres

Environmental temperature has a dramatic effect on water consumption. When temperatures rise, intake rises; the same applies when temperature drops, which can lead to increased incidence of impaction colic. The addition of salt to the diet will increase the horse’s desire to consume water.

Water temperature plays a key role in water consumption. Water around 10-18° C seems to be the sweet spot to encourage consumption. Studies have shown a drop of 38-41% when horses were offered near freezing water.

Aside from temperature, the freshness, purity, and palatability of the water also influences consumption. As a rule, water intake is directly related to dry matter intake, horses consuming all-hay high-fibre diets drink more water than horses fed a grain-based diet paired with hay.

Monitoring horses’ water intake on pastures can often be misleading, especially when pastures are lush. Green pasture grasses can be 65-80% water, which means many horses can consume much of their water requirement simply by eating pasture.

Water quality plays a major role in not just determining intake but also the health of a horse. Water quality is an important factor in water intake. Odours from minerals such as iron and sulphur, can negatively affect palatability. Temperatures below 5° C and over 30°C have shown significantly reduced intake. Colour seems to be more of an issue to humans than to horses. Regarding pH, water should be in the range of 6.5 to 8.5. If the pH is more acidic (less than 5.5), acidosis and reduced feed intake may occur. Highly alkaline water (over 9) may cause digestive upsets and diarrhoea.

Many types of algae are present in the water, one of the more prominent species is blue-green algae. If consumed in large amounts, blue-green algae can cause muscle tremors, respiratory distress, diarrhoea, among other issues.  Other algae can produce hepatotoxins which are toxins affecting the liver. Bacteria such as salmonella can be an issue in horses consuming poor-quality water, causing major health and reproductive problems.

How can we manage water quality?

Water quality management may be as simple as regular cleaning and maintenance of buckets and drinkers, or the addition of filtration systems. More extensive treatment options are available for those with problematic water. Testing of water provides a snapshot of your water quality which, when added to pasture testing and nutritional feed analysis can reduce vet expenses in the long run. If you do choose to test your water, find an accredited laboratory that is able to interpret results and provide advice.

Contact the Bluegrass Horse Feed Nutritional helpline for further advice.