Free feeding alfalfa to horses is generally not recommended. While alfalfa is a nutritious forage with real benefits, its high protein, high calcium content, and caloric density make unlimited access problematic for most horses. A better approach for most situations is feeding alfalfa in measured amounts, often mixed with grass hay, to get its benefits without the downsides.
Why Alfalfa Is Different From Grass Hay
Alfalfa packs significantly more nutrition per pound than typical grass hay. Its crude protein content runs around 127 to 142 grams per kilogram of dry matter, compared to just 79 to 88 grams in meadow hay. That’s roughly 60% more protein. The calcium content is also dramatically higher, at about 10 to 11 grams per kilogram of dry matter.
For a 1,100-pound horse eating 2% of its body weight in alfalfa hay alone, the daily calcium intake works out to roughly 124 grams with only 23 grams of phosphorus. That creates a calcium-to-phosphorus ratio of about 5.4:1. The ideal ratio for horses is 2:1, and while anything from 1:1 to 6:1 is considered acceptable, sitting near the upper edge of that range long-term is not ideal. Mixing alfalfa with grass hay brings this ratio into a much more comfortable zone.
The Calorie Problem for Easy Keepers
Free feeding works best with lower-calorie forages that let horses graze throughout the day without overeating calories. Alfalfa’s metabolizable energy sits around 5.5 MJ per kilogram of dry matter, and because horses find it highly palatable, they tend to eat more of it and eat it faster than grass hay. For horses that gain weight easily, or those with insulin resistance, this combination of higher energy and enthusiastic consumption makes free-fed alfalfa a recipe for obesity.
Horses with metabolic concerns are better served by lower-energy forages. Research comparing horses grazing different forages found that alfalfa and cool-season grasses produced higher glucose and insulin responses than lower-energy alternatives. If your horse is overweight or has been diagnosed with equine metabolic syndrome, free-choice alfalfa is one of the riskier feeding strategies you could choose.
Benefits Worth Preserving
None of this means alfalfa is bad. In controlled amounts, it offers genuine advantages. Alfalfa has a high intrinsic buffering capacity thanks to its calcium and protein concentrations, which helps neutralize stomach acid. Horses fed high-calcium, high-protein diets have been shown to develop fewer and less severe gastric ulcers. For horses prone to ulcers, feeding a flake or two of alfalfa before exercise or as part of a mixed hay ration can be protective.
Alfalfa is also an excellent calorie source for hard keepers, lactating mares, and horses in heavy work. These animals burn through energy quickly and benefit from the denser nutrition. For a thin Thoroughbred in training, free-choice alfalfa might actually be appropriate because the caloric surplus is exactly what the horse needs. Context matters enormously.
Enteroliths: A Serious Risk With Heavy Alfalfa Diets
Enteroliths are intestinal stones that form in the large colon when ammonium phosphate crystals build up in concentric layers around a small foreign object. Feeding alfalfa hay is a well-established risk factor for these stones. The high mineral and protein content of alfalfa creates the intestinal environment where enteroliths develop. Certain breeds, particularly Arabians and Morgans, appear more susceptible.
Enteroliths can cause colic and may require surgical removal. Horses in regions like California and the southwestern United States, where alfalfa-heavy diets are common, see higher rates of this condition. Limiting alfalfa to a portion of the total hay ration and ensuring the horse also eats grass hay significantly reduces this risk.
Excess Protein Affects the Barn, Too
When horses consume more protein than they need, the excess is broken down in the liver and excreted as urea in urine. Horses on forage-only diets (particularly high-protein ones) can produce 14 liters or more of urine per day. That urea breaks down into ammonia, which is the sharp smell you notice in poorly ventilated stalls.
High ammonia levels are not just unpleasant. In enclosed spaces, ammonia can irritate the respiratory systems of both horses and the people who work around them. Horses on free-choice alfalfa also drink more water to process the extra nitrogen, which means wetter bedding, more frequent stall cleaning, and higher overall management costs. If your horse lives in a stall for any portion of the day, this is a practical concern worth weighing.
Special Concerns for Growing Horses
Young horses have stricter nutritional requirements than adults, and getting the mineral balance wrong can contribute to developmental orthopedic disease (DOD), a group of conditions affecting bones and cartilage. High-calcium diets have been implicated in DOD, potentially by interfering with the absorption of other critical minerals like copper and zinc. Excessive calcium supplementation is a particular risk when young horses eat large amounts of alfalfa alongside a calcium-based supplement like ground limestone.
The recommended calcium-to-phosphorus ratio for growing horses is tighter than for adults, ideally between 1.1:1 and 2:1. A diet built entirely around free-choice alfalfa overshoots that range significantly. Foals and weanlings benefit from carefully balanced rations where alfalfa may play a role but does not dominate the forage supply.
When Free-Choice Alfalfa Can Work
There are horses for whom generous or even free-choice alfalfa makes sense. Lactating mares producing milk need the extra protein and calories. Horses in intense athletic work may need the caloric density. Severely underweight horses being rehabilitated can benefit from the rich nutrition. In these cases, the usual concerns about excess calories and protein become advantages.
Even in these situations, mixing alfalfa with grass hay at a ratio of roughly 50/50 gives you most of the benefits while moderating the mineral imbalance and reducing enterolith risk. Many horse owners find this blend works well: the alfalfa adds palatability and nutritional density, while the grass hay provides bulk and a more moderate mineral profile. You can offer this mix free-choice more safely than straight alfalfa, though monitoring body condition remains important for any horse with unlimited forage access.