Fats and oils have likely been used in equine diets for more than a hundred years, with the earliest mentions being for the benefit of adding shine or luster to the hair coat. More recently, owners have sought additional benefits of adding fat to horses’ diets, including weight gain, improved reproduction, milk quality, behavior, and performance.

Types of Fats to Feed Horses

Fats for equine diets can come from both animal and plant sources. Kathleen Crandell, PhD, equine nutritionist for Kentucky Equine Research, in Versailles, recommends fats from plant sources, such as canola and flax. “Corn oil used to be one of the most recommended supplements, but some recent studies have shown potential inflammatory issues within the body, possibly due to its high omega-6 content,” she says.

Oils, such as those from flaxseed/linseed, soy, canola, and fish, are higher in omega-3s, and owners are beginning to be use them more frequently. Brian Nielsen, PhD, PAS, Dipl. ACAN, professor of equine exercise pohysiology at Michigan State University, in East Lansing, cautions that not all sources of omega-3s are the same. “Fats that do not come from marine sources do not have Eicosapentaenoic acid (EPA) or and will likely not have the benefits the horse owner wanted,” he says.

Benefits of Fat in the Performance Horse

Both Crandell and Nielsen recommend increasing the fat content in performance horse diets because that population often has high caloric demands. “Adding fats is a great way to increase calories without increasing bulk,” says Crandell. On a pound-for-pound basis, fats provide more than two times the calories of grains such as oats and corn. This concentrated source of calories can reduce the overall volume of feed horse owners must offer.

“Another benefit of fat in the diet is a decreased thermal load within the body,” said Nielsen. The horse’s body produces less heat when it digests fats than other feedstuffs, especially those containing higher levels of protein or fiber. This can be advantageous for performance horses, especially those working in hot environments. High internal body temperature can have a negative effect on muscle cell function, so keeping core temperature lower or making it easier to keep it low can benefit the working horse.

Horses adapted to fat-supplemented diets will have more of the enzymes needed to use fats as an energy source, especially for long, slow, distance exercise, such as endurance. This means their body will use fats preferentially over stored muscle glycogen. Preserving muscle glycogen will increase the time it takes a horse to fatigue, so the horse should be able to perform at an optimal level for longer. Horses predisposed to having issues with muscle glycogen storage, such as those with equine polysaccharide storage myopathy, would also benefit from adaptation to a higher-fat diet. 

Research on the benefits of adding fats high in omega-3s to equine diets is a relatively new area. “Recent studies on the use of fish oils have shown beneficial anti-inflammatory properties, enhanced immune function, and improved quality of red blood cells,” said Crandell. “There are also indicators of benefits in horses with some respiratory issues, as well as skin allergies.”

Concerns About Feeding Fats to Horses

Not all fats are created equal, so consider a few factors before adding fat to your horse’s diet. For example, some horses might not like the taste of all fats, especially if the fats have gone rancid due to improper storage. A human might not notice the change as quickly as a horse, because the horse has a more sensitive sense of smell.

Because fats high in omega-6s, such as corn oil, could contribute to inflammation and inflammatory responses in the body mentioned earlier, they must be balanced with sources of omega-3 fatty acids to counteract the inflammatory response. Gamma-oryzanol, found in some supplements and rice bran oil, can purportedly help build lean muscle mass and also has antioxidant properties; however, some governing bodies prohibit its use in competition.

Are Fats Always Needed or Desirable in Horses?

In some instances a higher-fat diet is not in a horse’s best interest. Both Nielsen and Crandell do not recommend adding fat to the diets of horses that maintain weight easily. “Horses that have weight issues—yes, even with performance horses–do not need extra calories,” said Nielsen.

With some equine muscular conditions, such as myofibrillar myopathy, higher-fat diets can make the condition worse. Even though affected horses, including those with recurring exertional rhabdomyolysis and polysaccharide storage myopathy, can benefit from a higher-fat diet, Crandell said it is important to confirm the muscle myopathy before changing the diet.

How To Add Fat to a Horse’s Diet

Regardless of the type of fat used—top-dressed or already incorporated into a feed—introduce it gradually, over about two weeks. If top-dressing the feed with an oil, aim to add about ¼ cup to the feed every few days until you reach the desired amount. Evaluate your horse’s manure and, if it appears loose, gray, or greasy, reduce the amount of oil until the manure appears normal. If switching to a higher-fat feed, replace the current feed gradually, usually no more than ½ pound at a time, and increase the amount of new feed every three or four days. Keep in mind that the calorie content of fats is more than two times that of other calorie sources, so total feed intake in pounds per day will likely decrease.

Take-Home Message

You might consider adding fat to your performance horse’s diet for various reasons. It can boost the diet’s caloric density, decrease internal heat production, aid in thermoregulation in hot climates, and improve performance by sparing muscle glycogen and increasing time to fatigue. However, owners should be aware of the difference between fat sources before choosing one for their horses. As with all dietary changes, consult your veterinarian and an equine nutritionist before making adjustments.