GRAIN/CONCENTRATES In many cases roughage cannot provide enough nutrition for hard working horses, pregnant and lactating mares or growing youngsters. In these cases a concentrated form of nutrition is required. The most common for of concentrated feed is whole or crushed grains. A recommended quantity of grain is no greater than 1% of a horse’s body weight per day and preferably in two or more feedings with access to equal amounts of roughage. A higher percentage of grain, normally oats, are commonly fed to race horses.