Managing heat and hydration in the competition horse

As British summers and competitions start to hot up, managing heat and hydration becomes an essential part of caring for the dressage horse. While most riders recognise the importance of cooling and watering in heatwaves, dehydration and heat stress can quietly impact performance long before it’s outwardly obvious.

Understanding how horses regulate body temperature, and how we can support that process, is key to keeping them comfortable, healthy, and performing at their best.

Staying hydrated

The most important consideration in coping with the heat is ensuring hydration is maintained. Sometimes called ‘the forgotten nutrient’, water often feels like the most important part of the diet that we never mention. Essential to life, horses will typically be around 60% water, or 300L in a 500kg horse. That ratio is even higher in some of the most critical organs. Surprisingly, the lungs, often thought of as sacks of air, are around 90% water, which is essential for gaseous exchange and hence energy and power production. Meanwhile, brains are around 70% water, where its roles include cognitive function and signal transfer. This explains why one of the early signs of dehydration is a drop in performance and poor coordination.

So we can see that keeping horses hydrated is fundamental to performance.

Signs of dehydration:

Poor performance
Poor coordination
Lethargy
Sunken eyes
Depression
Strong colour / odour urine

Try these hydration tests:

Pinch Test – pinch the skin on the neck, when released it should flatten in <1 second.

Gum Check – gums should be moist and pink and turn white under finger pressure, returning to pink in <2 seconds on release.

A delayed response suggests reduced hydration and the need to take action.

Heat and sweat losses

Sweating is the horse’s primary mechanism for cooling, but sweat loss isn’t always obvious. Horses are efficient evaporative coolers, meaning significant fluid losses can occur before sweat becomes visible.

Work intensity, duration, humidity, travel and even standing in warm conditions can contribute to cumulative fluid loss over the day. As heat load increases, the demand for water and minerals rises accordingly, making proactive replacement essential rather than waiting for signs of fatigue.

Replacing what’s lost: electrolytes

Water is not the only nutrient lost in sweat, as it also contains essential electrolytes. These body salts are important for numerous pathways within the system, including muscle and nerve function, directly impacting performance. The most important electrolytes are sodium, potassium and chloride, though calcium and magnesium should also be included in full-spectrum rehydration.

For maintenance, a salt lick in the field and stable allowing free access self-supplementation, which horses will do for salt, is a good idea. However, this only covers maintenance requirements, and once the horse is working and sweating, they should be additionally supplemented with electrolytes.

A quality electrolyte supplement, such as NAF Electro Salts, can help restore electrolyte balance during periods of regular sweating. Broad‑spectrum formulations providing sodium, chloride, potassium, alongside calcium and magnesium, are most appropriate for working horses in warm conditions.

When selecting an electrolyte, it’s important to consider the ingredient list. A small amount of sugar (often dextrose) can aid palatability, but it should sit well below the salts in the composition listing, indicating that electrolytes, not sugars, are the primary component.

When and how to feed electrolytes

For harder work, pre-loading with electrolytes is advised, as that helps to create an internal reserve for them to draw on during travel and exercise.

When giving electrolytes it is essential that water is provided alongside. If you’re travelling and staying away regularly then training them to take electrolytes in water can help mask different tap water tastes and encourage drinking wherever you are.

Electrolytes can be fed:

Mixed into a small fibre‑based feed
Added to well‑soaked feeds to increase water intake
In drinking water for horses accustomed to this method, with plain water always offered separately

When to hydrate:

After any exercise, other than very low impact
One to two hours before travel, particularly to competitions
Between classes at competitions
For two to three days following intensive work or competitions
Whenever sweat loss is observed

Staying cool

Alongside electrolyte support, effective physical cooling is vital. Research supports rapid cooling of horses immediately after work, using liberal amounts of cool water applied over the whole body. Scraping is not essential as the priority is repeated application of fresh, cool water to allow continued heat dissipation.

Where hose access is limited, repeated sponging with generous volumes of water can be effective, provided it is applied over large areas rather than just the neck or quarters.

If you’re attending a show and you know the forecast to be particularly hot, then check with the organisers as to what they have in place to help you and your horse cope. If provisions are not sufficient then do consider not attending – your horse’s welfare comes first, and there is always another day.

When training at home, consider riding early in the morning or later in the evening to avoid the hottest part of the day. If this isn’t possible, adjusting the intensity of the session such as reducing duration, allowing more walk breaks, and being guided by how your horse feels and responds can help.

Managing heat and hydration successfully is about being proactive. By monitoring our horses closely, staying hydrated and replacing sweat losses, riders can beat the heat.

For free nutritional advice and further support on managing your horse in warm weather, contact NAF’s team.

Written by: Kate Hore, Head Nutritionist at NAF. RNutr (Animal), BETA ENFAR, R.Anim.Technol (Cert)

Reference

Schott H. and Lindinger M (2025). Fluid and electrolyte balance in exercising horses. 12th EEHNC Conference, Utrecht.

Zeyner, A., Romanowski, K., Vernunft, A., Harris, P. and Kienzle, E. (2014), Scoring of sweat losses in exercised horses – a pilot study. J Anim Physiol Anim Nutr, 98: 246-250