It’s easy to joke about your horse putting on a few extra pounds—after all, it isn’t going to hurt his feelings if you call him “the Chunkster” or some other affectionate nickname. But obesity in horses isn’t something to take lightly. Excess weight can have detrimental effects on a horse’s health, contributing to arthritis, insulin resistance and laminitis.

Obesity among horses is common. In fact, one study in England estimated that 54 percent of horses in that country are obese, a rate that is probably similar in this country. That makes obesity one of the most widespread health problems among horses today.

It can be difficult to slim down a fat horse, particularly one who is genetically predisposed to heaviness. It’s much better to prevent obesity. This requires an unbiased eye and vigilant management, but the payoff for the health of your horse will be immense. Here’s how you can do it:

1. Learn the body condition score (BCS) system.

Developed by Don Henneke, PhD, in 1983 as part of his doctoral research, the BCS system ranks, on a 1 to 9 scale, the amount of body fat a horse carries. Scoring a horse, however, requires more than a cursory look at his overall physique. Because fat is laid down in a predictable pattern, the locations of stored fat indicate the amount of excess a horse carries (see illustration below). And you cannot score a horse from a picture or even the other side of a fence—you have to feel areas of the body to get an accurate assessment, particularly in those whose visual anatomical landmarks are obscured by fat.

The BCS system will not only give you an accurate assessment of your horse’s current condition but will help you detect any changes as they develop. If you are unfamiliar with the BCS system or unsure you are using it correctly, ask your veterinarian to go over it with you. If you look up a BCS guide online, be sure it’s directly derived from Henneke’s system, because variations of it may not yield useful results.

2. Count the calories in concentrates.

Sweet feed and other concentrates provide essential calories to horses who need them—athletes, pregnant mares and the like. But they fuel weight gain in an easy keeper. Many horses don’t need any grain, yet receive a half scoop twice a day so they don’t feel left out at mealtime. This “kindness” only leads to obesity. If your horse is verging on being overweight, cut back his concentrates to a literal handful or none at all. You can add a supplement to ensure he’s still getting all the vitamins and minerals he needs and, of course, make sure he has plenty of hay to keep him occupied.

3. Rely more on hay.

It’s difficult (but not impossible) for a horse to become obese on an all-hay diet. As you cut back on your horse’s grain, increase his hay ration, providing 24-hour, free-choice access if possible. This not only is good for his digestion but helps reduce boredom. Some horses still gain weight on hay, particularly if it is rich. To compensate you can look for good-quality hay that is lower in calories or restrict your horse’s daily intake to 1 or 2 percent of his ideal body weight.

4. Control grazing.

Pasture is not the equine equivalent of salad. Not only will too much grazing put pounds on most horses, but it can trigger laminitis in those with insulin resistance or other risk factors. Grazing muzzles offer a relatively easy and effective way to control the amount of grass a horse eats without having to limit his turnout. If a grazing muzzle isn’t an option, consider designating a dry lot or very sparse pasture as the “fat field” and keep the farm’s easy keepers there during periods of lush growth or, for particularly at-risk horses, year-round.

5. Increase his exercise.

Activity is essential to keeping a horse’s weight in check. That’s not news to anyone. Unfortunately, the level of exercise your horse needs may come as a surprise. Casual riding on the weekends isn’t enough to make a difference to a horse who is prone to putting on weight. Even when he’s turned out full-time, he’s still not going to get the sustained exercise he’ll need to burn enough calories to offset even a modest diet. An easy keeper needs five or six sessions of targeted exercise per week, each lasting at least an hour and ending with him in a good sweat.    

If you can’t fit this amount of riding into your own schedule, start looking for help from a friend, an eager young rider or even someone interested in half-leasing your horse. Coordinate your schedules and ask your veterinarian to help you devise an exercise program that takes your horse’s current fitness into account and gradually improves his conditioning.