The best feed for your horse is good pasture. The second best choice is good quality hay. Most of us will feed hay for at least part of the year. You should be making every effort to buy the very best hay for your horse, as this will make up the greatest part of its diet. If you're feeding hay, it's really important to find out exactly now nutritious it is. This is done by sending samples of your hay to a lab and receiving a print-out of the nutritional values it contains. By knowing what is and isn't in your hay, you can determine which grains, concentrate or supplements you may need to give your horse to be sure its nutrition is balanced.
If your horse is working hard, is in foal, or is stressed or growing it may need a little extra energy. Sometimes, all that is required is extra helpings of hay, or longer grazing time. But more, or better quality hay may not always make up for all shortfalls in nutrition. This is when you may wish to feed either grains, or a concentrate mix that will have grains, beet pulp, minerals, molasses and other ingredients.
Reading the nutritional data and feeding instructions can feel like you're trying to interpret hieroglyphics. There will be an ingredients list that includes things like grains such as oats, barely, soy and whether they are crimped, extruded, rolled, cooked, cracked or flaked. You'll see ingredients like molasses that improves the taste and makes everything bind and mineral and vitamins. Some feeds contain forage—basically alfalfa or grass hay in pellet form.
The nutritional breakdowns are often expressed as percentages of your horse's recommended daily intake. Armed with your hay sample evaluation, you'll be able to calculate what you need to make up for with a concentrate. For example, if your hay sample indicated that it is low in selenium, which is common in most parts of North America, you'll know to choose a feed or supplement that will make up for that shortfall. More confusing are the percentages of crude fat, fibre and protein. To begin calculating these requirements you'll need know your horse's weight and activity level.
Unless your horse is on a rigorous show schedule or you're conditioning for a long distance trail ride, it probably doesn't need much more than hay or grass provides. Overfeeding is as unhealthy as underfeeding. If your horse is already a healthy weight, a mineral and vitamin supplement may be all that's needed. If your horse is working hard (most pleasure horses aren't) a concentrate formulated for extra energy may be needed. Broodmares may also need a little extra beyond hay—before and after the foal is born.
Using the information on the label, use your horse's weight and work load to calculate how many pounds of the feed to give. Increase portions slowly and never feed more than about 5lbs per feeding, to avoid colic. It's better to give two or three smaller portions a day, than one big one. Weighing feed is more accurate than measuring, although most of us use the 'coffee can' method after learning that the can will hold a certain weight of feed.
Generally, if you are feeding for weight gain or energy, you'll want a concentrate with a higher fibre and fat content. Growing horses may need more protein, but extreme caution should be used in feeding youngsters, as too rapid growth can cause serious problems. Feed companies try to make things easier for us by making up concentrates for different situations: performance horses, seniors, pleasure horses and broodmares.
Feeding straight grains is a little trickier. The nutritional content of grains such as oats, corn and barley can vary just as the nutritional content of hay can. Oats has been the grain most traditionally fed to horses. Whole oats retains more nutrition than rolled, cracked, crimped or steamed oats. Barley must be feed crushed and corn can be fed whole and has been the go-to grain when weight gain is desired. Corn has long been thought of as a 'hot food', but it's really not. It is possible to formulate your own grain feeding regime fairly accurately if you can get nutritional analysis of the individual grains. Here for example is Purina's breakdown of the nutritional content of oats. So the calculations for grain feedings are are done the same as a mixed concentrate. But again, all grains will vary in nutrition depending where they were grown, the maturity at harvest, weather and storage.