Written by Thomas Lenz, DVM, M.S., DACT
Courtesy of AAEP
The horse’s most vital nutrient is water. An adult horse’s body is composed of roughly 70 percent water, which equates to 770 pounds or 96 gallons of water for the average 1,100-pound horse. Foals’ bodies have even higher water content, roughly 80 percent, and on a weight-to-weight basis, small horses consume more water than large horses.
A horse’s daily water requirements are influenced by age; body condition; the amount, type and quality of feed consumed; fitness level; and activity level. Add to that the temperature, as well as the freshness, purity and palatability of the available water and it becomes obvious that there are a number of factors that influence water consumption. Because fat is low in water content compared to lean muscle, fat horses typically require less water than horses maintained at optimal body condition.
As a general rule, water intake is proportional to dry-matter intake, but the composition and digestibility of the feed is also a factor. Horses consuming all-hay diets drink more water than horses fed a grain diet coupled with hay or a complete pelleted diet.
Horses on good-quality pastures, which can be 65 to 80 percent water, will consume less drinking water compared to horses on hay and grain because a large percentage of their water needs are met by the moisture in the grass. That is why idle horses might actually consume less water in the summer than in the winter when they are stalled and on a hay-based diet. Their total water intake may be identical during both seasons, but just coming from different sources.
We all know that salt consumption increases thirst, but feed protein intake above the horse’s requirement increases both water intake and urinary output, as the horse voids excess nitrogen via urine.
An idle, 1,100-pound horse in a cool environment will drink 6 to 10 gallons of water per day. That amount may increase to 15 gallons per day in a hot environment. Work horses require 10-18 gallons of water per day on average but could require much more in hot weather. Nursing mares drink more water because of fluid loss associated with milk production and increased consumption of feed to support milk production. An 1,100-pound nursing mare can easily drink up to 20 gallons of water per day. Foals also have higher water requirements and will drink 6 to 8 gallons of water per day even in relatively cool weather.
A horse’s water consumption will also be greatly affected by the temperature of the water. Consumption appears to be best when the water temperature is between 45 to 65 degrees Fahrenheit.
Sudden weather changes can also affect water consumption and lead to problems such as impaction colic. To combat this, add an ounce or two of a loose salt to the horse’s daily ration when weather changes are imminent. The salt will stimulate water consumption.
Horses typically drink less water in cold weather, whereas heat and humidity increase their water requirements. In exercising horses, water intake may increase as much as 80 percent in horses moved from a cool climate to a hot, humid climate.
Depending on the conditions in which a horse is exercised, total water intake for an 1,100-pound horse can increase from a normal 4 to 10 gallons per day to as high as 30 gallons per day.
All horses need clean, good-quality water at all times. Outdoor water troughs should be cleaned at least every couple of week to remove debris and algae. Stall water buckets should be emptied and rinsed daily. Check automatic water systems daily, as they could malfunction and not be providing adequate amounts of water.