What is the food that gives a horse the highest energy?

Feed that is high in protein and carbs. There are some good brands on the market such as Omelene 300.

Feeds which produce the most energy for a horse are corn, oats, rice, maize, barley, milo, rice pollard, wheat pollard and compound feeds. Pre-mixed feeds and grains can be bought exactly for high energy release.

Soaked sugarbeet is also a brilliant energy food.