Although alfalfa is a great protein, vitamin and mineral source it should not be the only hay fed. Some owners choose to feed their horses straight alfalfa, but there is a downside.
Here are some things you should know if you choose to feed a straight alfalfa diet.
Protein in alfalfa runs between 15-18% or higher. Alfalfa is high in calcium which suppresses magnesium and it causes an imbalanced calcium to phosphorus ratio of 5:1. In order for that not to happen you must feed a supplement to balance out the ratio.
With the higher levels of calcium it results in an iodine deficiency which affects the thyroid. When the thyroid is not functioning properly it can cause things such as adrenal fatigue, hyperactivity, infertility, laminitis, founder and weight gain.
Horses that are low in magnesium will become flighty, nervous, cranky, tight, and sore. Magnesium is an important mineral because it is a major mineral in bone and is important for muscle contraction, relaxation and nerve transmission.
Feeding too much alfalfa can cause enterolith stones which can cause colic and blockages and lead to death of the horse.
Horse with allergies to alfalfa can develop edemas. I've seen horses with swollen legs and bellies. If your horse is on alfalfa and you see swelling (edema) consider taking them off of the alfalfa and see if it clears up.
Dr. Swerczek at the University of Kentucky proved reduced immune function on alfalfa diets by infecting two groups of horses with strangles. The grass hay-fed group did not become as ill and did not become carriers of the bacteria, while the alfalfa-fed group manifested more severe symptoms and became carriers.
If you're going to feed alfalfa you might want to consider buying it pelleted or cubed as the nutritional level tends to be more consistent. Make sure you buy from a reputable company as you don't want your horse eating any foreign matter like pieces of wire that have been found in some cubes.
By purchasing pellets or cubes you will have reduced storage requirements and they are easier to handle. Make sure they are green on the outside and not brown or black which indicates over processing.
The same holds true if you're going to feed baled alfalfa as you have to be careful so you don't buy any with blister beetles or get bales that are moldy.
Keep in mind that a horses need for protein is low. A mature working horse only requires about 12% protein. If you want to keep them working at an optimal level mix the alfalfa with a good grass hay.