Certain feeds are formulated without oats with no detriment to energy density. Many of these use other steam-flaked grains, super fibers, and fat-rich ingredients to make up for the energy deficit left by the exclusion of oats.

Because Pennfield Equine Feed Technologies offers a wide variety of scientifically formulated feeds, I am able to recommend mixing two of the company's feeds, EnduroEvent Ener-G and Fibregized Omega. Neither of these feeds contains oats, but EnduroEvent Ener-G includes easily digested corn among other high-calorie ingredients, so energy is plentiful. Likewise, Fibregized Omega contains beet pulp, rice bran, and soybean oil, all of which are calorie-rich. Gradual adjustments in the mixture offers flexibility in the diet: if an increase in energy is needed, more EnduroEvent Ener-G and less Fibregized Omega can be fed; and if a decrease in energy is indicated, less EnduroEvent Ener-G and more Fibregized Omega is appropriate. 

Remember that no single grain meal should exceed five pounds, so if the daily allotment of grain is ten pounds or more, consider feeding it in three or four smaller meals each day. For horses on high-grain diets, I would recommend the addition of RiteTrac, a gastrointestinal support supplement that protects the stomach from gastric ulceration and the hindgut from subclinical acidosis, a precursor to colonic ulcers.

Continue to feed high-quality hay on a free-choice basis, as this too will add calories to the diet. Because your horse is an athlete and probably sweats regularly, a salt block and perhaps even an electrolyte supplement might be warranted.