How much do you really know about this leafy green legume?

In some areas of the country, alfalfa is a regular part of life. It’s readily available and commonly fed, so it’s a logical foundation for many horses’ diets. In other areas, it is a delicacy of sorts, shipped in from different regions and bought a bale at a time on a vet’s recommendation to help certain horses that need nutritional support. For some types of horses—in either of those areas—-alfalfa simply isn’t a great choice. And, so, that fragrant green bale comes loaded with nutrients and, for some horse owners, a multitude of misconceptions.

Whatever your alfalfa experience, we’re here to tell you everything you need to know about this forage, starting with a little bit of history, and clear up any confusion about it.

Alfalfa Goes Way Back

Forage for horses can be divided into two categories—grasses and legumes. Grasses you’re likely familiar with include orchardgrass, timothy, and bermudagrass and are long and stemmy. Forage legumes, such as clover and alfalfa, are members of the pea family and, so, are cousins of peanuts and garbanzo beans.

“Alfalfa is a perennial legume, grown in most regions of the U.S. for horses and other livestock,” says Krishona Martinson, PhD, associate professor and equine extension specialist in the University of Minnesota’s Department of Animal Science, in Falcon Heights.

It was one of the first domesticated forages, planted and harvested in what is now Iraq, Iran, and Afghanistan several thousand years ago. Early farmers discovered its nutritional benefits, especially for hard-working horses, says Ray Smith, PhD, forage extension -specialist at the University of Kentucky (UK), in Lexington. “The main feed for horses of early armies in those regions was alfalfa,” he says.

“When alfalfa was first brought to the eastern part of the U.S. in the 1700s from Europe, it didn’t survive well—partly because of wetter soils and lower pH,” says Smith.

By contrast, when settlers brought alfalfa west in the 1800s during the California Gold Rush to grow livestock feed, it did quite well. “Use of alfalfa grew rapidly in the western U.S. as people realized it fit well with that climate” and less-acidic soil types, says Smith. “By the late 1800s and early 1900s we began to learn more about adding lime to low-pH soils, to make them more appropriate for growing alfalfa. Plant breeding was also beginning by the 1900s, and plant scientists were able to develop alfalfa plants that were better adapted to various soils in the U.S.” Modern plant breeding has also improved this legume’s disease resistance.

Today, alfalfa still grows best in well-drained soils rather than wet soils.

Which Horses Benefit From Alfalfa?

“The biggest benefit of alfalfa for horses is that it tends to be more nutrient-dense than most grasses when harvested at the same stage of maturity,” says Martinson. It typically contains more digestible energy, more crude protein and calcium, and fewer nonstructural carbohydrates (sugars and starches).

Because it’s so nutrient-dense, it is a good feed for underweight horses.

“It can also be beneficial to horses with muscle problems that are prone to ­tying-up (due to their increased protein needs) or horses with equine metabolic syndrome (EMS) due to the lower amount of nonstructural carbohydrates,” says Martinson.

She says alfalfa is ideal for horses on high planes of nutrition, such as lactating broodmares, growing horses, thin horses, racehorses, performance horses, or young foals that aren’t getting enough milk.

“With growing horses, however, use caution in amount fed, simply so they don’t grow too quickly or get too big too fast and become at risk for DOD (developmental orthopedic disease),” Martinson says.

We know that for horses sensitive to sugar or carbohydrates (e.g., horses with insulin resistance, pituitary pars intermedia dysfunction, etc.), building a diet on a good foundation of forage is especially important—the oats, corn, and barley that make up many feeds are 55-75% carbohydrate.

Some grass hays are also too high in sugar for these horses, and this is where a legume diet or mixed legume/grass diet can help lower total sugar intake.

Choosing the right hay for proper balance can be challenging, however.

For instance, a horse that’s overweight and insulin resistant needs a lower-sugar hay (the alfalfa), says Martinson, but not the additional calories, “So we often end up doing a mix where those horses receive some legume and search for a low-sugar grass hay to mix with it.”

“Many horse owners buy bales of alfalfa and bales of grass hay and feed several flakes of grass hay and one flake of alfalfa” as needed, says Krista Lea, MS, forage extension specialist and research analyst at UK. This can offer some cost savings if you also have horses that do fine on the less-nutrient-dense hay.

“I have three horses with three different nutrient requirements, so if I have different kinds of hay I can mix them appropriately for each horse—to get the right balance for what they need,” she says. You can add alfalfa pellets or cubes to a grass hay diet for the same effect.

Alfalfa is also suitable for horses prone to gastric ulcers, because the extra calcium acts as a buffer against stomach acid. You might offer performance horses alfalfa an hour or two before work or competition, during which acid can splash up into the nonglandular part of the stomach (where the cells of the lining do not produce protective mucus). The simple act of chewing creates more saliva, which also helps buffer stomach acid, says Lea.

Owners might also offer the legume to horses needing to develop more muscle, particularly along the topline. Stephen Duren, PhD, equine nutritionist and founder of Performance Horse Nutrition, in Weiser, Idaho, says this is because alfalfa provides amino acids needed for muscle regeneration. “We see this practice more in the East where a lot of marginal grass hay is fed.”

Beware of Blister Beetles

These flying insects—dead or alive—contain the toxin cantharidin, which can kill a horse if consumed in large amounts. Blister beetles feed on alfalfa blossoms and might swarm fields during harvest. Beetles killed by the haying equipment can end up in the hay.

Adult blister beetles emerge in June (sometimes a little earlier or later depending on the region and climate) to feed on alfalfa blooms. “These beetles tend to be more prevalent in late summer,” says Ray Smith, PhD, forage extension specialist at the University of Kentucky, in Lexington. “The first (and sometimes second) cutting of alfalfa almost never contains blister beetles because it is generally cut and baled ahead of when the adult beetles emerge.”

Years following drought typically see more blister beetles, as do central states such as Kansas and Oklahoma.

When purchasing hay, examine a few bales to see if the alfalfa has blooms. “If you always check the hay as you feed it, you can discard those bales or flakes that contain beetles,” says Smith. “The beetles will be very concentrated; if you find one or two you will usually find many.” He adds that 99% of bloomed hay won’t have beetles in it.

“Alfalfa producers who market hay for horses are aware of the issue of blister beetles,” he says. “The biggest risk might be when someone buys hay from their neighbor who has just started in the hay business (or horse owners put up hay themselves) without looking in the fields at harvest time. Always follow the recommendations in your state regarding scouting for and controlling blister beetles.”

—Heather Smith Thomas

Which Horses Should Not Eat Alfalfa?

Some owners believe alfalfa makes horses “hot,” but Martinson says there’s no scientific basis for this. “(It) does have more energy compared to grass hay of similar maturity, so perhaps a horse eating a lot of alfalfa in the absence of exercise may have more energy,” she says. “The biggest issue with alfalfa is weight gain in horses that don’t have adequate exercise.”

Additionally, it supplies more nutrients than most nonworking horses need, leading to obesity and its associated issues. So feed overweight horses or easy keepers just as you would the sugar- or carb-sensitive ones—offer them a mature grass hay with lower caloric content over a rich legume.

Alfalfa is a good source of nutrients for sport horses, but owners might want to avoid offering it when horses are working hard in hot weather, says Duren. Protein metabolism creates more heat than fat or carbohydrate metabolism. This added heat can impair the horse’s ability to dissipate heat. He might even suffer from dehydration (due to extra sweating and increased urination from the alfalfa breakdown/flushing from the kidneys) and be more likely to experience heat stress.

“Extra protein cannot be stored in the body like extra fat or carbohydrates and must be excreted,” says Duren.

A horse eating more protein than the body can use will also drink more water (to help flush out the additional waste products). This creates more urine and, thus, more ammonia odor. 

“Ammonia in stalls can irritate airways and make horses susceptible to respiratory problems,” says Duren. “This is especially true with foals, since they are smaller and spend more time lying down. Ammonia is heavier than air and concentrated near ground level.”

While feeding extra protein is wasteful, a high-protein diet in itself does not hurt a healthy horse. It can be detrimental, however, to horses with impaired kidneys or liver. These individuals have problems processing and excreting protein and should be kept on a very low-protein diet.

Duren also doesn’t recommend feeding straight alfalfa to endurance horses due to its protein and calcium content. The last thing you want on an endurance ride where the horse is sweating for long periods is the increased body heat, water needs, and urine production described. High levels of calcium, on the other hand, can interfere with the horse’s ability to mobilize bones’ calcium stores during exercise. Endurance athletes can benefit from small amounts of alfalfa, just like any other performance horse, says Duren, but make sure it’s not their sole forage source.

“Many performance horses are not worked to the point of dehydration, so they can handle a higher percentage of alfalfa,” he says. “In California there are many cutting, reining, and other performance horses that eat a lot of alfalfa hay (due to its wide availability) and balancer pellets, and that’s their entire diet and they do fine.”

Not all alfalfa hay is really high in potassium, but you have to test it to find out.

Dr. Stephen Duren

Other horses that do best with limited alfalfa are horses with the genetic muscle disease hyperkalemic periodic paralysis (HYPP). These horses are affected by hyperkalemia, or an excessive amount of potassium in the blood, which causes their muscles to contract more readily than normal and makes them susceptible to sporadic episodes of muscle tremors or paralysis. These horses are particularly sensitive to alfalfa’s high potassium content.

“Potassium levels in forage are dependent on what the plants are pulling out of the soil, however,” says Duren. “It can make a difference how and where the alfalfa was grown and whether it was fertilized with manure—which really drives the potassium levels higher. If I had a horse that was sensitive to potassium, rather than exclude alfalfa per se, I would have the hay analyzed. Not all alfalfa hay is really high in potassium, but you have to test it to find out.”

Some horses with unpigmented skin should not eat alfalfa because they could be prone to photosensitization caused by black blotch disease, says Martinson. This is a mold that causes black blotches on the undersides of the leaves of legumes, including alfalfa. “Horses ingesting this mold may experience excessive ­sunburn—which seriously affects unpigmented areas of their bodies,” she says.

The more serious issue with these horses, however, is the liver damage from the toxins in the mold.

Selecting Alfalfa Hay

When looking for good-quality alfalfa, be sure it’s clean with no dust or mold—just as you would with any hay. Also aim for a good leaf-to-stem ratio (most of the nutrients are in the leaves; the stems are more fibrous). “It should be a green color, meaning there are more leaves and the hay is not weathered or rained on before it was put up,” says Smith.

If your horse doesn’t need the high nutrition value of pure alfalfa, look for a mixed grass/alfalfa hay. To determine the nutrient content of any hay, have it tested. Maturity, harvest conditions, soil conditions, and more can affect protein, energy, and mineral levels, says Smith.

Even after you’ve selected good hay, it pays to check it for dust, mold, weeds, foreign objects, blister beetles, and dead animals as you feed it.

Poisonous weeds that sometimes grow in alfalfa fields include ragwort, groundsels, Johnson grass, Sudangrass, water hemlock, and hoary alyssum. To steer clear of these, buy hay from a reputable person or company that knows how to grow alfalfa weed-free.

Take-Home Message

When incorporating alfalfa into a horse’s diet, plan for the animal’s specific nutritional needs. Your feed salesman, veterinarian, and nutritionist can help you put together a balanced ration and recommend for or against feeding this forage.

“A lot of horse owners are intimidated by alfalfa and think they shouldn’t feed it, but it is a great feed for horses,” says Martinson. “Owners just need to manage the diet carefully … and make transitions to and from alfalfa slowly.”

Author: Heather Smith Thomas