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Understanding Dehydration

Managing your horse's water in the hot summer months

The hot summer months have arrived; it is time to consider the impact of the warmer conditions on your horse. Water makes up slightly more than 65% of a horse's body. An average horse that is not being exercised requires the bare minimum of five gallons a day. Exercise and climate increase this need, as sweating is the main means by which horses lose heat. It is possible for water intake to increase by 300% during heavy, prolonged exercise on a hot day, therefore ten gallons of water should be available per horse at all times. Sweating also causes the loss of electrolytes, such as sodium, potassium, and chloride, which are essential for fluid balance, nerve and muscle function, and acid base chemistry. If the lost electrolytes are not replaced, the horse's ability to perform is impaired. Dehydration, along with the loss of electrolytes, can cause the horse to exhibit signs of fatigue, weakness, trembling, pain, stiffness, tying-up, thumps (diaphragmatic flutter) and even colic.

Evaporation of sweat on the skin surface accounts for up to 70% of heat loss during exercise. A horse can lose 3.2 gallons of moisture an hour through sweating, and thus a great deal of water must be consumed to compensate. A substantial amount of evaporative heat loss also occurs through the lungs and nasal passages.

The success of heat loss is affected by the relative humidity. When the air is dry evaporation is more efficient. Sweat will quickly evaporate during dry weather. When it is humid the skin surface remains wet and sweat will drip from the body, removing very little heat as it drips, although it is removing water and electrolytes.

Without replacement of these losses, the horse will become dehydrated and develop electrolyte imbalances, both of which can adversely affect performance. Decreases in body electrolyte content also suppress the horse's thirst response, thus worsening the level of dehydration, particularly with continued exercise and sweat loss. It is not difficult to determine when a horse has become dehydrated. The skin loses it elasticity, mucous membranes are dry, and the eyeballs can appear sunken.

There are many strategies to prevent dehydration. Using common sense is of primary importance. Provide plenty of fresh clean water at all times, including during and after exercise. Once your horse has caught their breath (a few minutes) it is ok to offer water. Some form of salt supplementation is a must. Horses on hay or pasture usually are in excess of daily potassium requirements, but not sodium and chloride.

A commonly used strategy is to provide a salt block. However voluntary salt intake is highly variable among individual horses. An alternative is to top dress a salt supplement on the horse's grain ration. There are numerous electrolyte supplements on the market. Read the product labels and take note of the actual quantities of sodium, chloride, and potassium, avoiding supplements that contain a lot of sugar and not much else. The supplement should also contain calcium and magnesium to aid in prevention of muscle cramping and thumps. Administration of electrolyte pastes before and during prolonged exercise is also safe and efficacious. Another key point is ensuring that the horse has access to water after administration of the paste. Some horse owners have success in training their horse to drink mildly salty water (i.e. one ounce/gallon h20). A guide as to how much salt should you give your horse, is approximately 2 ounces a day in a moderate climate and up to 5 ounces in hot humid months.

Fitness will also aid in combating dehydration. A horse that is well fit has a stronger heart thus allowing the beats per minute to decrease. A larger volume of oxygen being delivered to the cells, and will lessen the load on the heart. A conditioning program is also a benefit to the respiratory system. A fit horse is far less apt to suffer from fatigue of the respiratory muscles.

Nutritional fitness is critical in prevention of dehydration. The more a horse works, the more energy from feed it will require. The large intestine is a fluid reservoir, which is drawn on during exercise. Therefore it is beneficial to feed a diet high in fiber to help maintain hydration during exercise.

As any conscientious horse person can see it is critical to avoid dehydration and the problems associated with it. Even the fittest horse can be pushed to exhaustion, if proper rest, water, and diet are not provided. When a suitable program is put in place and a horse is given the tools to stay hydrated your horse will perform his best.