Alfalfa can be an excellent addition to most horses’ diets, even for those who 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. But some people just don’t want to feed alfalfa; they believe it causes laminitis. And after years of working with horses, it appears that it may, in fact, lead to laminitis in some horses. I found this to be very puzzling since alfalfa is low in sugar and starch, even lower than most grass hays. Its high protein content, however, makes it more caloric, which can be a problem for IR horses who need to lose weight. But I always included some, albeit a small amount.
Nevertheless, there appears to be something about alfalfa that troubles some IR horses. After giving this considerable thought, I believe I can shed some light on why this may be the case. 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
Excess protein - quality vs quantity
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 (e.g., blood, lungs, heart, liver, skin, bones, joints, etc.). There are 22 amino acids, of which ten are considered essential -- they cannot be produced within the horse’s body or they cannot be produced in adequate quantity to meet the horse’s need. For a protein to be of high quality, it must contain all of the essential amino acids in proper proportion. Plant protein sources are potentially limiting in the essential amino acid, lysine. When lysine is low, protein synthesis comes to a halt. The National Research Council (NRC) has established lysine requirements for all horses. As of yet, requirements for the other nine essential amino acids have not been quantified, though recent research has shown that threonine may be the second limiting amino acid. To ensure your horse has an ample amino acid pool in his bloodstream from which to synthesis proteins within his body, 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. If you’d like to do it yourself, table 1 offers suggestions on alternative whole foods that can be incorporated into a grass-based diet.