Follow these eight tips to increase your horse’s weight and muscle mass

You don’t know how lucky you are,” your barnmate says as she leads her muzzled and overweight horse out to his small paddock. “I’d give anything for Sammy to look as lean and lanky as your horse!”

If she only knew you were working (and spending) double time to try to put weight and muscle mass on your four-legged charge. It’s a different challenge than shedding pounds, but adding condition to a horse can be just as daunting.

We reached out to Bob Coleman, PhD, PAS, an associate professor and equine extension specialist at the University of Kentucky, in Lexington, and Clair Thunes, PhD, an equine nutritionist who owns Summit Equine Nutrition, in Gilbert, Arizona, for guidance. Here are their tips.

1. Be sure your horse actually needs more condition.

While this advice might seem obvious, obesity remains a serious problem in horses. In a 2012 study, Virginia-Maryland Regional College of Veterinary Medicine researchers found that 32.3% of 300 horses were overconditioned (had a body condition score, or BCS, of 7 on the 1-to-9 scale) and 18.7% were obese (BCS of 8-9).

In a 2016 study, Australian and British researchers determined that 23.1% of 229 Australian pleasure horses and ponies were obese. They also determined that “owners perceived their animals to be in significantly lower body condition compared with the researchers’ assessments.”

Essentially, many of us believe our horses need to gain weight when, in fact, they’re in good condition. Coleman says a BCS of 4 to 6 is likely appropriate for most horses. If your horse falls in that range (see TheHorse.com/184488 for help assessing your horse’s BCS), he probably doesn’t need to gain much, if any, more weight. If you’re still not convinced, consult your vet or an equine nutritionist.

2. Rule out other health issues.

Some horses are simply too lean or they’re underconditioned and need to gain weight and/or muscle mass. But weight loss and muscle wasting can also be signs of potentially serious health conditions, from dental disease to pituitary pars intermedia dysfunction (equine Cushing’s disease). Have a veterinarian examine your horse before you begin a weight gain regimen to ensure he has no underlying health problems. Getting a health issue under control might also help your horse put on pounds.

3. Know how much you’re feeding.

To improve body condition or muscle mass successfully, you need to recognize the exact amount you’re currently ­feeding—both in forage and concentrates.

“Feeding requirements are calculated in units per day, so horse owners need to know pounds of hay and concentrate, not flakes and scoops,” Coleman says. “Know how much a bale weighs and how much a scoop holds. Not knowing this can easily lead to both over- or underfeeding.”

4. Increase forage first.

Once you’ve confirmed your horse does need to gain weight, start by increasing the amount of good-quality hay in his diet.

“The best forage is one that is free of mold and dust, has nothing in it that could be an issue, such as toxic plants, and the forage needs to be palatable,” Coleman says. “If the horse won’t eat it, then it does not do much good.”

Also consider the nutrients the hay provides. “A legume hay such as alfalfa is going to be higher in digestible energy and crude protein than a similar-maturity grass hay,” he adds.

If a horse needing weight doesn’t have alfalfa in his diet, Thunes says she might recommend adding it because it typically offers more calories per pound than grass hay. If the horse already has alfalfa in his diet, she often recommends increasing the amount of grass hay, since she prefers to keep the alfalfa portion to 25-30% of the total forage ration. Some horses, however, such as those with the genetic muscle disease hyperkalemic periodic paralysis (HYPP), should not consume alfalfa due to its high potassium levels.

Be sure your horse is receiving the recommended amount of forage (both hay and grass) in his diet—typically 2% of his body weight. (If your horse is kept on quality, not overgrazed, pasture for 50% of the time, he’s likely consuming about 1% of his body weight and would need the rest in hay.) Then increase that amount slowly, and “feed what they need,” Coleman says.

5. Increase other rations second.

If increasing hay portions doesn’t add the desired body condition, you might need to add calories from another source.

“A performance horse, for example, is going to need a certain level of calorie intake to meet their requirements; it is difficult to do that on an all-forage diet,” Coleman says. “Start with the forage at a reasonable intake, and then supplement it with a suitable concentrate to meet the calorie and other nutrient needs.”

Thunes says this concentrate might not need to be a grain; she often uses other easily fermentable fibers.

“What types of concentrates I prefer depends on the individual horse,” she says, “but my typical go-to is a concentrate feed with fermentable fiber such as beet pulp or soy hulls plus supplemental fat.”

The appropriate concentrate or fiber depends on a variety of factors, from the horse’s job and age to health issues. For example, some concentrates have starch and sugar contents over 20-25%. This could cause serious issues for metabolic horses. And beet pulp with added molasses isn’t suitable for horses with HYPP. Consult a nutritionist or veterinarian if you don’t know what type of concentrate to choose or you’re concerned about potential issues with grain or fiber sources.

Additionally, while a horse might need more concentrates to gain condition, large grain meals can result in other problems, including colic, an acidic hindgut, gastric ulcers, and laminitis. To combat these risks and help optimize digestion, aim to feed several smaller meals (4 to 5 pounds for a 1,000-pound horse) and limit starch intake to 2 grams per kilogram of body weight per meal.

6. Add supplements.

Another way to boost calorie intake but minimize starch and sugar consumption is to add a fat supplement—whether it’s oil or a commercial product—to the horse’s diet. This additive can help increase body fat stores.

But Coleman says you first need to determine what it is you want to accomplish: Is it simply adding body condition, which is related to fat stores, or do you want to increase muscle mass, which involves proteins?

The horse’s body generates fat when calorie intake exceeds calorie usage, Thunes explains, “so throwing more calories at a horse that is already in good weight but undermuscled could just get you a fat horse that is undermuscled.”

To help improve muscle mass, Thunes says she uses “high-quality protein supplements that are utilizing whey protein, which provides a source of branched-chain amino acids, specifically leucine.”

And, Coleman adds, don’t forget exercise if you’re trying to build muscle mass.

7. Be patient.

Gaining weight and muscle takes time. Coleman says he’d expect to start seeing results in 30 to 45 days.

“Horses are not really designed to gain weight rapidly,” he says. “Horse owners need to appreciate the microbial ­community that lives in the horse’s digestive tract and give them time to adapt to feed changes (abrupt shifts in hindgut bacteria can cause you to lose ground). Going a bit slower can help horse owners reach their goals faster.”

If you don’t start seeing results after a month or so, revisit the possibility of underlying health issues, Thunes adds.

“I would be looking to see if there is something else going on that hasn’t been addressed,” she says. “Does the horse need dental work? Does it have ulcers or some other gastrointestinal disruption that negatively impacts feed utilization? How about internal parasites? Is a vitamin E deficiency impacting ability to build muscle? I would suggest reaching out to a veterinarian to cross these things off.”

8. Readjust the diet as necessary.

Once you’re happy with your feeding program results, reevaluate your horse’s diet. It won’t necessarily change, but you might need to make occasional tweaks to maintain your horse’s ideal weight.

“As your horse approaches the desired BCS, you can hold off on any increases in feed and maintain the intake levels that helped the horse get there,” Coleman says.

There might come a point, however, when the horse no longer needs all the calories you fed to add condition.

“If they start to head toward being too heavy, you have to pare the calories back first by reducing concentrates and grains,” Thunes says. “Be careful when you do this, however. If you reduce the amount of a fortified feed, ensure you are still feeding enough to meet the horse’s vitamin and mineral needs. If your reductions take you below the manufacturer’s recommended daily intake level, you will need to add some amount of a ration balancer to make up the shortfall.”

Take-Home Message

To increase your horse’s body condition and muscle mass, Thunes recommends going back to basics: “I think sometimes these horses end up on very complicated diets because owners are drawn to try all kinds of things, and they don’t work,” she says. “It’s worth stepping back and asking if you could get more done with fewer total products. The answer is often yes.”

All the while, evaluate your horse to head off problems before they become too serious. “Monitor BCS and body weight frequently to help you manage your horse,” Coleman says.