Horses are grazing animals designed to obtain nourishment by eating fiber-rich forage. With the domestication of horses, meals have evolved to include a combination of grass, hay and processed feeds. Performance, racing and high-strung light breed horses often require high-energy feeds to maintain healthy body conditions.

Conversely, draft breeds, even working draft horses, require less energy than their smaller counterparts.

“When it comes to daily calories, draft horses require slightly less calories pound for pound than a comparably sized light horse,” said Beth Valentine, DVM, Ph.D., an expert in draft horse nutrition and professor of anatomic pathology at Oregon State University College of Veterinary Medicine.

The way a draft horse’s metabolism functions accounts for the most significant difference. “Draft horses have a slower metabolism than riding horses. They are more even tempered and have a different fight or flight instinct,” added Michael R. Stone, DVM and owner of Oak Haven Belgians in Fremont, Ohio.

“There is a general consensus that while a draft horse may eat more than a light horse because they are larger animals, their energy requirements are lower on a pound for pound basis,” said Kathleen Crandell, Ph.D., an equine nutritionist at Kentucky Equine Research.

Estimating rations

Rations for all horses are determined with mathematical formulas. For light horse owners, Valentine said that you can estimate the daily calorie needs for your draft horse(s) by the calorie intake of similarly sized light horses. An accepted standard of calorie intake in relation to body weight exists for light horses. Using the accepted light horse standards, the target calorie total is multiplied by 0.75 to determine the daily needs for draft horses.

“As an example, the maintenance diet of a 1,000 pound light horse is 15,000 calories per day,” she said, adding that “the maintenance diet for a 2,000 pound draft horse is (2 ×15,000) × 0.75 = 22,500 calories per day.”

A chart of standard daily caloric requirements has been developed and is available in Valentine’s book, “Draft Horses: An Owner’s Manual.” “There is a table of estimated calorie needs for light horses and draft horses published in the book,” she said.

Once you identify the calories your draft needs to maintain his body condition, it’s important to translate that into the pounds of forage (hay and grass) the horse needs each day. Typically, draft horses need between 1.5 percent and 2.5 percent of their body weight in forage. “For example, if your draft horse weighs 2,000 pounds you multiply that by .015. That equals a minimum of 30 pounds of forage on a dry matter basis the horse needs each day,” Crandell said.

Some draft horses can thrive on hay and or grass without needing a feed. Good quality hay will go a long way in meeting your horse’s nutritional needs. “I personally like feeding high quality grass hay with some alfalfa mix,” Stone added.

Draft horses that are able to maintain healthy body conditions on pasture and hay alone often require additional supplements to compensate for minerals and vitamins lacking in the forage. Many areas in the United States have soils that are deficient in selenium and low in other trace minerals like copper and zinc. However, it is important to work with your veterinarian to determine the appropriate amount for your horse. Providing too much selenium can be toxic. “A good mineral supplement or a ration balancer can help provide the other trace minerals as well as selenium,” Crandell said.

Valentine often recommends additional vitamin E even for horses kept on pasture and or alfalfa products, which are naturally high in vitamin E content. “Extra vitamin E never hurts and sometimes helps. I recommend 1 IU vitamin E per pound of horse each day,” she said.

In addition to concentrates that compensate for lacking minerals or vitamins, some horses may need additional supplements. “If hoof quality is an issue, I recommend a hoof supplement with methionine as well as biotin,” Valentine said.

Working horses that are pulling or straining to move heavy loads may benefit from joint supplements. “The key is to only use supplements when they are needed,” Crandell noted.

Special considerations

“As it turns out, two-thirds of all draft related horses are ‘metabolically different’ and prone to developing a muscle issue known as equine polysaccharide storage myopathy (EPSM, also called EPSSM and PSSM),” Valentine said.

“Equine polysaccharide storage myopathy is an abnormal glucose metabolism in the horse which leads to excessive glycogen storage in muscle cells,” Stone said. “Clinical signs are similar to tying up.”

The disease can also be found in other breeds such as draft crosses, warmbloods and quarter horses. Symptoms can vary among breeds. Before much was known about the condition, it was called “Monday morning sickness.” The biggest challenge with EPSM in draft horses is that the animals are stoic and symptoms can be subtle. Clinical signs include muscle soreness and weakness in muscles. Left untreated, the condition is potentially fatal.

During research in 2000 Valentine discovered that EPSM is strongly linked to nutrition. “These horses need a high fat and fiber, low starch and sugar diet,” she explained. “Alfalfa, hay pellets, senior feeds or other low starch and sugar commercial feeds are best.”

“For a horse with recognized EPSM issues, I recommend adding 1 pound of fat per 1,000 pounds of horse each day,” she said.

The least expensive method of doing this is by adding soy, canola or corn oil. “Two cups of oil is 1 pound of fat. You want to introduce the fat slowly and increase it gradually,” she suggested.

Even horses that have not been diagnosed with EPSM can benefit from added fat. For non-EPSM horses, she recommends adding at least ½ pound of fat per 1,000 pounds of body weight each day. Crandell cautioned that ” feeding dietary fat to a horse that is already overweight may exacerbate a condition, insulin resistance, which is common in obese horses.”

Plentiful turnout and consistent exercise are important components to managing horses diagnosed with EPSM. “These horses do better with regular, steady work,” Stone said. “It’s best to avoid giving long bouts of stall rest and then a quick return to work.”

Learn more

Draft horses are generally considered “easy keepers” in comparison with their light horse counterparts, requiring fewer commercial feeds. Despite needing fewer calories to maintain a healthy body condition, it’s important to recognize the metabolic differences between draft horses and light horses.

Understanding EPSM, its symptoms and triggers are keys to keeping draft horses healthy. Work with your regular veterinarian to develop a daily ration that meets all of your horse’s needs. Genetic testing is available to determine whether a horse has EPSM.

This test looks for a change in a GYS1 (glycogen synthase 1) gene, which identifies some, but not all EPSM horses. A negative test does not necessarily rule out EPSM. Muscle biopsy, or a response to diet change, can identify these GYS1 negative EPSM horses. Once diagnosed, diet and exercise changes can take nearly four months to take effect. “All too often the first sign of a problem is when it is too late. That is why I recommend this type of diet for all draft-related horses,” Valentine concluded.