Feeding a miniature horse is similar to feeding a standard equine, in the sense that one size does not fit all. Most minis do well on a hay-only diet, but broodmares and working minis may require grain. Because obesity is a big problem for these tiny horses, limit the feeding of treats. Minis should always have access to clean, fresh water.
Grass hay makes up the bulk, if not the entirety, of your mini's diet. If your mini is primarily a pet and does no work, hay alone should suffice. Avoid alfalfa -- it's too rich for minis. A horse should consume about 1 percent of his total body weight daily, and that holds true for minis. If your mini weighs 200 pounds, give him 2 pounds of hay daily, divided into morning and evening feedings. Weigh your mini using a measuring tape -- or a livestock scale if one is available -- so you know his exact size. Even for experienced horse people, it's easy to underestimate or overestimate a mini's weight. Your vet can advise you whether your mini is underweight, overweight or just right, so you can target an optimal weight.
Minis are prone to laminitis, often triggered by consuming rich grass. This serious hoof issue can lead to permanent lameness or require euthanasia. Either limit the time your mini spends with access to pasture, or put a grazing muzzle on him so he can't overeat. Unless your field is very poor quality, it's not wise to allow a mini all-day access to pasture unless he's muzzled.
Miniature Horse Feed
If your vet advises you to feed grain to your mini, avoid simply giving your animal a small amount of regular horse feed. Obtain commercial feed designed specifically for minis. These feeds contain less sugar and starch than standard feeds, and are nutritionally balanced for little equines. Feed according to package directions, taking the weight of the animal, stage of pregnancy or lactation, and workload into consideration. Transition your mini to grain over a period of one week to 10 days.
Miniature Horse Supplements
If you want to add some additional shine to your mini's coat, Michigan State University Extension advises giving your pet 1 daily teaspoon of ground flaxseed. If you feed grain, check the product's ingredients before adding flax seed, as it may already be mixed in. If you don't want to feed grain but want to ensure that your mini receives sufficient vitamins and minerals, your vet can recommend a suitable vitamin/mineral supplement fed in lieu of grain.