Alfalfa is commonly fed to horses in many areas of the country, although less is fed in Texas than some other areas due partly to the concern with blister beetles in Texas-grown alfalfa. Like many other hays, alfalfa's nutrient quality depends on its maturity at harvest; the time of highest quality occurs before it is overly mature. Dr. Pete Gibbs from Texas A&M indicates that alfalfa is richer in nutrients than some other roughages and it is a good source of crude protein, fiber, and calcium. Alfalfa may have 30 percent higher crude protein than grass hays. Although alfalfa is more expensive than grass hay, it may be less expensive when you consider the higher amount of protein. Alfalfa has a 6:1 calcium to phosphorus ratio and this can help balance cereal grains because they are generally higher in phosphorus; feeding alfalfa means you don't have to buy other mineral supplements to feed your horse.
Some alfalfa is treated with preservatives to increase storage life, and in most cases the preservatives are not dangerous for horses. Chopped alfalfa is also available and has been shown to have nutrient digestibility that is higher than that of average-quality chopped roughage. It works well for feeding horses that need additional protein, such as young growing horses and brood mares. Pelleted alfalfa is also available and can be added into a grain mix. Lesser amounts of pelleted alfalfa can be fed than long-stem alfalfa because the pellets contain a larger portion of rich leaves. If pellets are fed and no pasture is available, additional long-stem roughage should be fed to discourage bad habits such as wood chewing. Alfalfa cubes can also be mixed with grain based feeds and used when certain horses need supplemental feeding.
However, there are times when alfalfa is not recommended. Dr. Catherine Whitehouse from Kentucky Equine Research indicates that it is not recommended in all cases. One concern of feeding alfalfa to foals is potential for contributing to orthopedic disease. Although developmental orthopedic disease has multiple causes, high-energy diets like in alfalfa can contribute to this problem. High-energy diets can be related to physitis, which is inflammation of the growth plates adjacent to a joint, that can lead to lameness and pain so if this develops, feeding alfalfa is not a good option. Replacing alfalfa with good quality grass hay is a good option for these foals as grass hay generally has less calories.
However, you have to be careful, as lots of grass hay grown for dairy cattle may also have too much energy for some horses and this is especially true for overweight horses and those that are insulin resistant. These horses should not be fed alfalfa or even premium quality grass hay but should be fed low to moderate quality grass hay. Premium quality grass hay will have an abundance of leaves and pliable stems with a rich color. However, if you have horses that are insulin resistant due to a hormonal condition, the hay needs to be tested for nonstructural carbohydrates before feeding because you cannot tell the difference by just looking. If you are not sure about feeding your horse, consult with your equine veterinarian.