Dehydration causes decreases in performance and if more serious, health problems that lead to shock and death. Minimal daily needs for water have been estimated at 5 to 8 gallons for a mature idle stock horse; however, many factors increase this need. As daily losses of water increase, so does the need for replenishment.
One of the major factors affecting how much water a horse needs is the amount a horse loses through sweat and respiration as a result of exercise. These losses are affected by the amount of exercise, the environmental temperature and humidity, and how adapted the horse is to the exercise. Exercise causes the horse’s body to produce large amounts of heat. This heat must be released from the body as it is produced. Otherwise, bodily processes fail and life threatening conditions, collectively termed heat stress and heat stroke, result. A horse sweats to cool its body. Estimates are that as much as 60% of the heat that is generated by exercise is lost through sweat.
Water needs can increase 400% over maintenance estimates when horses are working in hot, humid environments. Under maximal working conditions, horses can lose as much as 4 gallons of sweat per hour. Even at more normal working levels, 10 to 15 pounds of water weight can be lost. These levels, if not replaced, can dehydrate the horse’s body to critical levels. Lower levels of unreplenished losses may not be life threatening, but might be the limiting factor to athletic performance. Even water losses as small as two to four percent of body weight has shown to negatively affect human athletic performance.
As such, water intake, and the monitoring thereof, is one of, if not the most important nutrient concern of exercising horses. Recommendations are fairly simple: provide a horse a continual supply of fresh, palatable water at free choice levels. The only time it is recommended to possibly restrict water intake is immediately prior to exercise and during immediate recovery from exercise when heart and respiration rates are highly elevated. At these times, limiting water intake to small amounts given frequently may guard against any potential digestive upset from water intake. As many of our athletic competitions require periodic use over several hours, it is also important to encourage horses to drink small amounts frequently during the periods between exercise bouts.
Disruptions of a horse’s routine schedule, interaction with unfamiliar horses and surroundings, and changes in water source can cause voluntary decreases in water intake. Several techniques have been used to encourage finicky horses to drink: flavor aids, ensuring salt intake, hand watering, and transporting water supplies from the source the horse is accustomed to drinking. Regardless of how finicky, trainers and owners are recommended to keep accurate accounting of water consumption while at events. Disruption of normal drinking patterns is a sign of impending problems and decreased performance.
Reprinted with permission from David W. Freeman, OSU Extension Equine Specialist