Feeding alfalfa hay and pasture to the average horse will most likely result in significant weight gain. However, forage (hay and/or pasture) should be the backbone of a horse’s diet, with at least two-thirds of the diet being some type of forage. Alfalfa is an excellent forage for most livestock, but the forage quality of good alfalfa hay and pasture exceeds the nutritional needs for most horses. The average adult horse (lightly worked or ridden) needs about 10% crude protein in its diet. The crude protein in most good-quality alfalfa hays and pastures vastly exceeds 10%. Although feeding excess protein to horses does not result in any short-term health problems, it can lead to strong-smelling urine (a concern if the horses are stalled in a barn) and can contribute to weight gain. If buying hay, hay with higher protein levels usually demands a higher price. Numerous horse owners are paying premiums for protein that is not needed by their animals.

Alfalfa hays and pastures also have higher digestible energy (DE) compared to grass hays and pastures. DE is used to balance the energy portion of a horse’s diet. Again, feeding alfalfa hay and pasture to the average horse will probably cause it to gain weight. Horse health problems tied to excessive weight gain include Cushings, metabolic syndrome, laminitis or founder, and insulin resistance. The potential for excessive weight gain is the major drawback for feeding a high quantity of alfalfa to horses. Mares that are lactating or in late-term gestation, or horses that are in an intensive training program, would most likely benefit from adding some alfalfa to their diets because of the increased energy.

Calcium (Ca) and Phosphorus (P) are critical to bone and tissue formation in horses. For the average adult horse, the Ca:P ratio should be between 3:1 to 1:1. A benefit of having alfalfa as part of your forage is that alfalfa hays and pastures tend to have higher calcium levels relative to phosphorus, and have higher Ca levels than most grass hays and pastures. It is important to have your forage and grain tested to ensure the Ca:P is adequate and never inverted, especially in young, growing foals.

Not only will horses gain weight on pastures with a high quantity of alfalfa, but there are also pasture management practices to consider. Horses are selective grazers and some research studies have shown that horses prefer alfalfa over grasses in a pasture. In a mixed grass – alfalfa pasture, horses will actually choose to continuously graze the alfalfa, while leaving the grasses. However, most varieties of alfalfa will not withstand continuous grazing and will be short-lived in a pasture. To extend the life of alfalfa in a pasture, choose a variety that is recommended for grazing and make sure to rest the pasture and allow regrowth.

Bottom line, alfalfa is an excellent forage, but should not be fed (as the sole forage or in high quantities) to the average adult horse because of the potential for excessive weight gain and the negative health effects tied to weight gain. Feeding alfalfa (not usually as the sole forage, but in higher quantities) can be useful for classes of horses that require additional energy, including lactating mares and horses in intensive training programs.

Krishona Martinson, PhD
Extension Educator
University of Minnesota Extension
763-767-3842
bjork026@umn.edu