The following information on water intake in horses is provided by the nutrition experts at Kentucky Equine Research.
Some horses visit the water trough frequently for a drink; others sip from time to time through the day; and still others enjoy splashing and playing with the water, but don’t seem to drink very much of it. In general, horses consume more water in hot weather than in cooler seasons. They also drink somewhat less when they are grazing pastures in spring and early summer because the lush grass contains a large percentage of liquid. Horses eating mostly dry hay need to consume plenty of water to ease the passage of intestinal contents and avoid impaction. During the winter months, some owners give their horses a grain mash (grain mixed with water) in an attempt to increase total water intake.
A study reported in the University of Minnesota Horse Newsletter was designed to evaluate the practice of feeding grain mashes to horses during the winter months. The study was conducted at the University of Wisconsin, River Falls. Ten mature horses divided into two groups were used in the study. In the winter trial, the horses were kept in individual stalls in a heated barn, while in the autumn trial the horses were housed in an unheated barn. For both trials, the horses were given a pelleted concentrate at 0.5% of their body weight. The feed was offered either dry or mixed with a quart of water per pound of feed (approximately one liter of water per 0.5 kg of feed) to form a slurry or mash. The horses were also given alfalfa hay (lucerne) twice a day. At every feeding, each horse was given 8.5 gallons (approximately 36 liters) of water. Before each feeding, unconsumed feed and water from the previous feeding were measured.
Overall, horses consumed significantly less water in winter than in autumn. Horses on the mash diet consumed more water during the winter trial, but this difference was not seen in the autumn trial. Mash-fed horses tended to drink as much as, or more than, horses fed dry grain, in addition to the amount they consumed as part of the mash. Results of this research indicate that feeding mashes does tend to help in getting horses to drink more water during the winter.