Summer takes a toll on us all. With temperatures circling the century mark almost anywhere in the U.S., we should all be mindful of how this affects our horses. Most trainers in the Southwest will start working horses about 3 a.m. these days just to avoid the worst of the heat. Even with all The Big Ass Fans® beating the air into submission, while the misters blow a cloud of haze through the cattle pens, man and beast alike cannot fully escape the heat. The best we can hope for is to ride it out, so in an effort to do so, let’s look some of the basics in equine hydration.
In the adult horse, upwards of 2/3 of its entire body is water. For foals, this number is more around the 80 percent mark since they tend to have a greater body surface area than mass. The intake of water can come in two forms: 1) Actual liquid water and 2) Water that is produced from metabolic activity.
All chemical reactions produce molecular water and carbon dioxide. Water can be taken in only by two forms, but lost in four different ways. Moisture can be lost through the respiratory tract, across the skin as sweat, as urine excreted by the kidneys and through manure. Oddly enough, about 75 percent of water loss in a horse is through the manure, with only the fine control done through urine.
The necessary water intake depends on diet, work load and environmental temperature. This can range from 15-20 liters a day up to 90 liters a day, depending on your situation. Maintenance requirements, that is just the amount needed to sustain bodily functions in a horse, is 50-100 ml per kilogram of body weight per day. So, just to be safe, let’s say a 1,000-pound horse will need about 45 liters per day. A gallon is roughly 3.75 liters, so that equals 12 gallons of water just for maintenance. This number does not include losses from heat, sweating or riding.
Hydration is the key for maintaining blood volume, cardiac perfusion, tissue perfusion, oxygenation, balancing specific electrolytes and acid-base balance within a horse. Signs of dehydration are dry mucus membranes, decreased skin elasticity, decreased urine output and weakness. Those are all somewhat non-specific signs of illness in any horse, so staying ahead of the curve is extremely important in the summer time.
Dehydration can be categorized as mild at 5-7 percent, moderate at 7-10 percent, and severe at >10 percent of total body weight. The scary thing about dehydration is that even to the most trained eye, clinical signs are not evident until they approach 5 percent of bodyweight. That’s a 20-liter deficit before you ever know something is wrong.
So as the temperature stays up and our plan to use horses for work and pleasure continues right along with it, do not underestimate the necessity of hydration. Just because you feel fine doesn’t really mean your horse does as well. Important electrolytes like sodium, potassium and chloride are lost in large amounts through sweat. Those three simple elements control a huge percentage of bodily functions in your horse and need to be replaced right along with the total fluid volume of water.
Electrolyte supplementation is every bit as important as offering extra water throughout the day. I prefer supplementing electrolytes in feed rather than water, as it will increase water intake, without the need for the horse to drink a larger volume of water containing an electrolyte solution.
You can lead a horse to water, but you can’t make them drink, right? Right. But not too many horses will turn their noses up at feed, so add the electrolytes there and they will lead you to the water.
Dr. Justin High is a veterinarian and partner in Reata Equine Hospital in Weatherford, Texas. He graduated vet school from Texas A&M University and completed an internship at The Littleton Equine Medical Center in Denver, Colo. High’s years of practice focuses on the Western performances horse. Send any comments or questions to firstname.lastname@example.org.