In the wild, horses live only on roughage, and they innately know how to get the nutrients they need by seeking out specific herbs and grasses — in other words, horses do not need grain to thrive. In the domesticated life of the horse, grain is more accurately a supplement, making up for what dry forage cannot provide in nutrition. Except for the horse that cannot eat hay for health reasons, such as allergy or heaves, hay should be the main source of nutrition for the horse.

However, horses typically cannot eat enough dry, bulky hay in the course of a day to get the nutrition they need if the hay is of mediocre quality or if the horse has a heavy workload. This is where grain steps in to fill in the nutritional and energy gaps. In some areas of the country, horses are fed oats, corn, and mixes of whole grains. Most backyard horse owners rely on commercially manufactured horse feeds that have been designed to balance the nutrient intake when added to a recommended amount of hay.

Mixed Grain

Grain mixes can come with or without molasses (the addition of molasses gives the grain the designation of “sweet feed”). Manufacturers usually have many different mixes in their line of premixed grain. The major difference is often in the percentage of protein. Some are actually “complete” feeds that, if forage is not available, could be fed as the horse's entire ration if given in sufficient quantities.

What Kind of Grain?

You should pick a brand of grain that is easily accessible. When you buy your horse, find out what he is eating. If he seems to be doing well with it and maintaining good body condition, you may as well stick to it. If you have other horses or if you cannot find the brand he was eating through your nearby grain store, you can switch to a different brand. You will probably find a similar mix in all brands. Always change gradually over the course of a week, mixing the new brand with the old brand, and slowly increasing the amount of the new until you've made a complete switch.

Complete Feeds

Most grain manufacturers offer a feed that contains some roughage and can be fed as a complete feed without hay if it is fed in sufficient quantities. Complete feeds often come in pelleted or extruded form, but they also can come as loose mixes.

A horse that relies on complete feeds as her entire ration with no hay may be more prone to exhibit unwanted behaviors, such as chewing wood. This is thought to result from the frustration caused by an innate need to eat roughage and simply keep busy by grazing. After all, horses evolved to be grazing herd animals.