The Importance of Water to the Horse

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Consultant nutritionist for British Horse Feeds, Dr Tom Shurlock, talks us through the importance of water for the horse and advises on how we can ensure our horses stay hydrated.

Did you know… Water makes up to 70% of the horse.  

It has been described as the forgotten nutrient, and is critical to every single aspect of life, health and wellbeing. 

Water in the Body 

Water provides the base of all nutrition; it delivers saliva, stomach acid, the enzymes of the small intestine and the fermentation capability of the hindgut.  

It forms a layer along the length of the gut, through which the absorption of nutrients is initiated; it provides the medium for chemicals to cross the gut wall – either through or between the cells – and is the transport mechanism throughout the body, both in the cardiovascular and the lymphatic systems.  

Water also provides the medium in which all metabolic and biochemical reactions are conducted and carries the waste out of the body. 

Beyond nutrition it carries oxygen to (and carbon dioxide from) every cell, allowing the diffusion of these gases across the cell membranes. It transports hormones, immunoglobulins, antibodies and all the components that regulate those essential metabolic factors. It is integral in secreting substances onto the outer surface of the skin, and hair, to maintain a barrier against infection, parasites and other pathogens. 

Water also helps maintain body temperature, through evaporative heat loss of sweat, and breath, cooling the horse during exercise and in warm temperatures.  

At the other end of the scale, heat loss due to cold weather can be mitigated by giving warm water to drink, or feeding a warm soaked mash, carrying warmth to the body core. 

In short, water is not important, it is essential! 

Water Balance 

Like every living system, water balance is a matter of constant regulation, fine tuning and replenishment. Water loss, for whatever reason, needs to be matched with water intake, and it is the rate of loss which ultimately drives the system.  

Too much intake is relatively easily sorted – increased urination – but too little creates a whole range of problems and degrees of severity. 

The body balancing water

The horse is very efficient at water acquisition; the gut contents passing through the upper digestive tract is remarkably liquid. Up to 100 litres of water is present in the gut – ingested, and also added via saliva, gastric acid, enzyme secretions – and most of it is resorbed in the hindgut.  


Where ingested water fails to meet the body’s needs, the first casualty is the moisture in the gut; this can lead to impairments in gut content travel and gut motility, which could potentially lead to colic. 

The next stage is dependant on the horse’s response; in order to conserve body moisture there is reabsorption through the kidneys and a reduction in loss through the urine. At the same time mechanisms are activated that reduce loss of moisture as sweat. However, these are short term mechanisms and can be damaging through rise in urine concentrations in the plasma and reduction in heat loss. 

Increasing levels of dehydration will impact on the bloodstream, reducing fluidity that can lead to heart failure, oxygen starvation and multiple organ dysfunctions. Muscular activity fails. Finally, the cells themselves become flaccid and lose moisture leading to biochemical breakdown. 

Extreme dehydration will lead to death fairly rapidly. 


Providing access to adequate water will negate the threat of dehydration but the main problem is ensuring there is an adequate intake.  

It is calculated 5-7% of a horse’s weight is needed as a daily intake. On top of this, water loss through exercise, urine, faeces and temperature control needs to be taken into account. Hard exercise, for example, can lose up to 15 litres per hour which, for an endurance horse can soon mount up. 

Although it would be advantageous in these circumstances, it is not possible to store a water reserve. Homeostasis is such that excess water is quickly voided, and shortfall needs to be made up reasonably quickly.  

Luckily, for the base state of a horse – grazing, limited exertion – there is enough water inherent in grass to cover needs; it is for the housed, hay fed animal, or heavily exercising that water becomes a need.  

The most obvious and practical way around this is to provide a water bucket, as long as it is kept full. 

There are a few drawbacks though. The potential of being knocked over or contaminated both may reduce water intake. Secondly, the horse may not drink sufficient amounts; if the water is too cold, or there simply is not enough, then mild dehydration may occur.  

And thirdly, water not bound within the matrix of fibre may be absorbed too quickly and voided before rehydration is completed. Although this is unlikely in the majority of situations, feeding a well-soaked fibre will help introduce extra water into the horse without it consciously drinking. 

Hydrating fibre mash
Well-soaked mashes are ideal for hydration.

Water should be considered as the essential nutrient, and should be present in the daily diet at around 2-3 times the dry matter fed. As grass easily covers this, as would haylage or soaked hay, a bucket feed as a top-up might suffice. Once other demands are added, the use of moist feeds should be considered, so drinking remains a top-up.  

Did you know… Speedi-Beet holds 5 times its weight in water and Fibre-Beet holds 3 times its weight in water – the ideal hydrating fibre source with guaranteed hydration every feed.