Alfalfa is by far the most important legume hay for horses. It is the most widely fed, most commercially available, and most nutritionally dense legume forage in the equine world. With roughly 13% crude protein on a dry matter basis (compared to about 8% in typical grass hays) and more than double the calcium content, alfalfa fills nutritional gaps that grass hay alone sometimes cannot. But it is not a perfect fit for every horse, and knowing when to use it, how much to feed, and what to watch for matters just as much as knowing its benefits.
Why Alfalfa Stands Out Nutritionally
Alfalfa hay delivers about 127 to 135 grams of crude protein per kilogram of dry matter, while meadow hay typically provides only 79 to 88 grams. That protein difference is meaningful for horses with higher demands: growing youngsters, pregnant or lactating mares, and hard-working performance horses. Calcium levels tell a similar story. Alfalfa contains roughly 1% calcium on a dry matter basis, while grass hays sit closer to 0.4% to 0.5%.
Under USDA grading standards, the highest quality alfalfa (“Supreme” grade) contains over 22% crude protein, while “Premium” grade falls between 20% and 22%. These top grades reflect hay that was cut early, has a high leaf-to-stem ratio, and retains good color. Most horse owners will encounter hay graded somewhere below these tiers, but even mid-quality alfalfa significantly outperforms grass hay in protein and mineral content.
One thing to keep in mind is the calcium-to-phosphorus ratio. Alfalfa runs about 1.27% calcium and 0.24% phosphorus, creating a ratio of roughly 5:1. The ideal ratio in a horse’s total diet is around 2:1, with anything from 1:1 to 6:1 considered acceptable. This means alfalfa on its own sits at the upper edge, and a diet made entirely of alfalfa could push the ratio higher than ideal once other feeds are added. Blending alfalfa with grass hay or balancing it with feeds that contribute more phosphorus keeps things in range.
Stomach Ulcer Protection
One of alfalfa’s most practical benefits is its ability to reduce gastric ulcers, a problem that affects a large percentage of performance horses. The high calcium and protein in alfalfa act as natural buffers against stomach acid. In a study at Texas A&M University, horses fed alfalfa hay alongside a concentrate were dramatically less likely to develop ulcers than horses fed Bermuda grass hay with the same concentrate. Alfalfa prevented ulcer formation in 11 of 12 horses, while only 3 of 12 horses eating Bermuda grass stayed ulcer-free.
The physical form of the hay helps too. Long-stem alfalfa requires extensive chewing, which stimulates saliva production. Saliva is a natural acid buffer in the horse’s stomach. On top of that, the fibrous mat of hay sitting in the stomach physically shields sensitive tissue from splashing gastric acid, particularly during exercise. This is why many trainers feed a flake of alfalfa before riding.
Horses That Benefit Most
Alfalfa is especially valuable for horses with caloric or protein demands that grass hay cannot meet on its own. Lactating mares producing milk need significantly more protein and calcium, and alfalfa covers both. Young, growing horses benefit from the amino acid profile. Senior horses that struggle to maintain weight often do well with alfalfa added to their diet because it is calorie-dense and palatable. Horses in moderate to heavy work burn through calories quickly, and replacing a portion of grass hay with alfalfa can help maintain condition without dramatically increasing grain.
Underweight or hard-keeping horses of any age are common candidates. Because alfalfa is energy-rich relative to grass hay, it can help put weight on without the digestive risks that come with feeding large amounts of grain.
Horses That Should Avoid or Limit Alfalfa
Not every horse should eat alfalfa freely. Easy keepers, meaning horses that gain weight on very little feed, can become obese on a straight alfalfa diet. The extra calories and protein simply are not needed, and excess protein gets excreted through urine, creating ammonia-heavy stall conditions.
Horses diagnosed with Hyperkalemic Periodic Paralysis (HYPP), a genetic muscle disorder most commonly found in Quarter Horse bloodlines, should avoid alfalfa entirely. Alfalfa is high in potassium, and HYPP horses need total dietary potassium kept between 0.6% and 1.5%, with individual meals containing less than 33 grams. UC Davis specifically lists alfalfa hay as a feed to avoid for these horses.
Enteroliths, intestinal stones made primarily of magnesium ammonium phosphate, are another concern. Research from California found that horses fed 50% or more of their diet as alfalfa had a significantly higher risk of developing these stones. Alfalfa raises the pH of the large intestine, creating the alkaline environment in which enteroliths form, and supplies the magnesium and nitrogen that serve as building blocks. Horses with a history of enteroliths, or breeds known to be at higher risk (Arabians and Morgans, in particular), are typically transitioned to grass hay with daily pasture access to reduce recurrence.
Blister Beetle Contamination
A risk unique to alfalfa is blister beetle contamination. These insects contain cantharidin, a toxin that irritates and damages the lining of the digestive and urinary tracts. As few as 25 ingested beetles can be toxic to an average-sized horse, and the beetles do not need to be alive to be dangerous. They are often killed and trapped in alfalfa during the harvesting process, particularly when hay is crimped or conditioned.
Blister beetles are more common in southern and central states and tend to swarm in alfalfa fields during mid to late summer cuttings. First cuttings carry the lowest risk. Buying from a reputable source, inspecting hay before feeding, and asking your supplier about their pest management practices are the best ways to minimize exposure.
Clover: The Other Legume Hay
Red clover and white clover are the other legumes occasionally found in horse hay, either intentionally planted or as volunteers in mixed grass fields. Clover provides decent protein and is palatable, but it carries a specific risk that alfalfa does not. Red clover is susceptible to infection by a fungus called Rhizoctonia leguminicola, which produces a toxin called slaframine. Horses eating contaminated red clover develop a condition commonly known as “slobbers,” marked by excessive, dramatic salivation. In more severe cases, respiratory distress and frequent defecation can occur.
Slobbers typically resolves within a few days of removing the contaminated hay from the diet. It is rarely life-threatening, but it is alarming to witness and can lead to dehydration if prolonged. Because of this risk and because clover is less consistently available in pure stands, it has never achieved the same status as alfalfa in horse feeding programs. Most clover that horses consume comes as part of a mixed grass-clover hay rather than as a standalone product.
How to Feed Alfalfa Effectively
For most adult horses in light to moderate work, alfalfa works best as a supplement to grass hay rather than the sole forage source. A common approach is feeding a diet that is 25% to 50% alfalfa and the remainder grass hay. This captures the protein and calcium benefits while keeping the overall calcium-to-phosphorus ratio balanced and reducing the risks associated with high-potassium, high-nitrogen diets.
Horses with higher nutritional demands, like lactating mares or horses in heavy training, can tolerate a larger proportion of alfalfa, sometimes up to 100% of their forage. In those cases, monitoring body condition, hydration (excess protein increases water needs), and stall hygiene becomes more important. Alfalfa-fed horses urinate more frequently and produce stronger-smelling urine because their kidneys are clearing the extra nitrogen.
When shopping for alfalfa, look for hay that is leafy, green, and free of excessive stems, dust, or mold. Leaves hold most of the protein and calcium, so hay that has lost its leaves during baling is nutritionally diminished. A slight sweet smell is normal. Musty or sour odors indicate mold, which should never be fed to horses regardless of the hay type.