Is it OK to feed alfalfa to an insulin-resistant horse?

Hoof Nutrition Intelligence is a twice-a-month web segment that is designed to add to the education of footcare professionals when it comes to effectively feeding the hoof. The goal of this web-exclusive feature is to zero in on specific areas of hoof nutrition and avoid broad-based articles that simply look at the overall equine feeding situation.

Below you will find Part 1 of the latest question and answer installment that you can share with your footcare clients.

Q: Is it OK to Feed Alfalfa to an Insulin-Resistant Horse?

By Juliet M. Getty

A:  Alfalfa can be an excellent addition to most horses’ diets, even for those that are insulin resistant (IR). I often recommend feeding it because it boosts the overall protein quality of a grass-hay diet and, in general, enhances the horse’s muscle tone, immune system and overall health.

Yet some people don’t want to feed alfalfa because they believe it causes laminitis. But after years of working with horses, I’m convinced it may lead to laminitis in some horses.

I found this situation to be very puzzling since alfalfa is low in sugar and starch, even lower than found in most grass hays. However, its high protein content makes it more caloric, which can be a problem for IR horses that need to lose weight. But I still include a small amount of alfalfa in the ration for these horses.

Nevertheless, there appears to be something about alfalfa that troubles some IR horses. I believe there are two plausible reasons, both leading to excess blood glucose and the concomitant secretion of insulin:

1. Excess protein in the diet
2. Preservative often sprayed on alfalfa hay

All proteins consist of long, branched chains of amino acids. Upon digestion, amino acids are free to enter the blood stream and travel to individual tissues where they are recombined in a very specific order to produce the protein needed by that particular tissue (blood, lungs, heart, liver, skin, bones, joints, etc.).

There are 22 amino acids, of which 10 are considered essential that can’t be produced within the horse’s body or not available in adequate quantities to meet the horse’s need. For a protein to be of high quality, it must contain all of the essential amino acids in the proper proportion.

Plant protein sources are potentially limiting in the essential amino acid, lysine. When lysine is low, protein synthesis comes to a halt. While the National Research Council (NRC) has established lysine requirements for horses, but there are no official requirements for the other nine essential amino acids. However, recent research has shown threonine may be the second limiting amino acid.

To ensure a horse has an ample amino acid pool in its bloodstream from which to synthesis proteins, it is best to feed a variety of protein sources to improve the quality while not overdoing the quantity. Commercially fortified feeds often include a variety of ingredients to create quality protein.

Protein quantity becomes a problem when the horse is overwhelmed with amino acids. If large amounts of protein are consumed beyond the horse’s need to replace and repair body proteins, excessive amounts of amino acids can’t be stored for later use and are destroyed. The metabolites of amino acid degradation can potentially lead to excess glucose in the blood.

It’s easy to overwhelm the horse with too much protein when feeding alfalfa hay since it typically contains more than twice the amount of protein as many grasses. Since individual grass and alfalfa hays will vary significantly, it’s always best to have your hay analyzed, as excess protein from any source can lead to excess insulin secretion.

When baled during wet or humid conditions, alfalfa is often sprayed with buffered propionate (also known as propionic acid) to retard spoilage This preservative not only reduces mold, but also decreases drying time in the field, thereby diminishing the potential for leaf loss from harvesting and providing more baling flexibility.

Not considered to be harmful, propionate is one of three volatile fatty acids (VFA) naturally produced by the hindgut bacteria during hay fermentation. The other two VFAs are acetate and butyrate.

These VFAs serve as a significant energy source for your horse. Acetate is utilized by many tissues including the heart, muscles and the brain. Butyrate provides energy for the cells that line the hindgut epithelium. 

Propionate is a major precursor toward glucose production through a process known as gluconeogenesis, which is a problem for the IR horse. Once propionate is absorbed and metabolized, it is converted to glucose. So when you feed alfalfa that has been treated with propionic acid, you are essentially increasing your horse’s blood glucose level, just as you would if you had fed hay containing a large amount of sugar and starch. Increased glucose levels lead to increased insulin.

Too much protein can be a concern for the IR horse and it’s easy to exceed the horse’s protein requirement when adding alfalfa to the ration. Alfalfa itself is not the issue, but rather the contribution it makes to the protein content of the entire diet. Since protein quality is important, consider adding smaller amounts of alfalfa or add different protein sources to better stay within limits. In addition, try to avoid alfalfa that has been treated with propionic acid.

Juliet M. Getty, PhD, is an independent equine nutritionist with a wide U.S. and international following. Located in Lewisville, Texas, her research-based approach optimizes equine health by aligning physiology and instincts with correct feeding and nutrition practices.

Click here to read part 2 of the June 15, 2020 installment of Hoof Nutrition Intelligence: How do I Determine the Cause of the Poor Quality Hooves with my 4-Year-Old Quarter Horse Gelding?

Click here to read more installments of Hoof Nutrition Intelligence.