Q. I have an ulcer-prone mare that I’ve always fed a forage-first diet with a vitamin supplement mixed with hay pellets. When I’ve fed concentrates in the past, she’s developed gastric ulcers. Now I’ve started training her for endurance and feel she needs more calories for this higher-intensity work. I’m curious about grain-free feeds for horses. What does grain-free mean? Does it mean low-starch? If they aren’t providing calories from grains, where is the energy coming from?

—Via e-mail

A. The Association of American Feed Control Officials defines grain as seed from cereal plants. For example, oats, barley, corn, and wheat—in their intact forms—would be classified as grains as they are all seeds from the respective plants. Wheat middlings, however, would not be classified as a grain as it is not the whole seed. Rather, “middlings” is specifically a term used to describe “a by-product of flour milling comprising several grades of granular particles containing different proportions of endosperm, bran, (and) germ, each of which contains different levels of crude fiber.”

Therefore, a feed could be labeled as grain-free (not containing the whole seed) but still contain ingredients derived from grain parts, such as wheat middlings. Removing whole grains from feeds typically results in a significant reduction in starch, and ingredients such as wheat middlings have become popular because these ingredients contain less starch than the entire grain but provide similar calorie levels. This enables feed manufactures to provide feeds with the higher calories for performance horses while controlling starch intake.

Ingredients such as wheat middlings are not, however, starch-free and, while grain-free feeds typically have lower starch contents, they might not be as low as necessary for some horses, especially those with metabolic issues. Therefore, it is always important to find out a feed’s non-structural carbohydrate (NSC) content if this is an important consideration for your horse, even when its labeled grain-free.

Other common ingredients used in grain-free diets to increase the feed’s calorie level include fermentable fibers, such as sugar beet pulp and soy bean hulls, as well as fat sources such as rice bran and vegetable oil. These would be good choices of fuel for a horse participating in endurance as they support the type of aerobic exercise endurance horses typically perform.

Of course, rice bran and sugar beet pulp can be fed very successfully on their own. However, a good vitamin/mineral supplement would be necessary to ensure the diet is meeting all your mare’s nutrient needs, especially trace mineral and vitamin E. A commercial grain-free feed has been properly fortified so, when fed correctly according to the manufacturer’s recommended feeding rates, you won’t have to supply any further vitamin or mineral supplements.

You’re right that veterinarians and nutritionists generally recommend reducing the amount of high-starch grain fed to ulcer-prone horses. Still, some level of starch in the diet can be beneficial for hard-working horses. The key is to only feed small amounts at a time, stretch high-starch meals out throughout the day, and not feed more than 1 gram of NSC per kilogram of body weight per meal per day.