There seems to be a lot of controversy and mixed feelings about feeding alfalfa to horses, particularly horses with a metabolic condition. I get this question quite often and I am glad that I have the research and knowledge available to me from Dr. Thomas to help explain it all.
Alfalfa is an excellent source of protein for horses, and while it should not be fed to an IR horse in hay form as the main source of roughage, feeding pelleted or cubed alfalfa as a dietary supplement is perfectly safe. Alfalfa has a very low glycemic index, which is also important to consider for an IR horse. Alfalfa has been shown to have “buffering” effects on stomach acid which may reduce the chance for ulcers. It can also be very helpful for a horse that is a “hard keeper”, as it has a high caloric value. It’s also very palatable, making it easy to get your horse to eat. Be careful when switching to alfalfa as it sometimes will cause digestive upset, but this is most commonly caused by a sudden change in the diet, not the alfalfa itself. It’s best to make the change slowly as you would in any other dietary change, over a two-week period. It will take about this long for the digestive system to adjust to the new “food”. If anything, you may notice a few days of “looser” stools. Because it does provide a significant number of calories, exercise caution when feeding to an already overweight horse. A good exercise program should be implemented in these cases.
Feeding alfalfa in hay form can be a huge “trigger” for an IR horse who has had laminitis. According to Dr. Thomas’ research, alfalfa and any high protein food will stimulate an intestinal polypeptide whose function is to “signal” the pancreatic beta-cells to secrete more insulin into circulating blood, for use during “active” movement. Since horses with a metabolic dysfunction, such as Insulin Resistance, Equine Metabolic Syndrome, or “Cushing’s” already live with hyperinsulinemia (elevated serum/blood insulin), eating alfalfa hay will increase the already high insulin level. This will heighten the risk for a laminitic event, and if the horse is already laminitic, could greatly increase damage to the hoof.
Because a large number of metabolic horses are also overweight and alfalfa hay contains a lot of calories per pound, feeding them alfalfa hay would exacerbate the weight issue. It is difficult, if not impossible, to feed enough alfalfa hay to meet their daily dry matter intake needs without maintaining the current overweight condition. It also would not help them lose any excess weight.
For a horse that is not metabolic, feeding alfalfa hay is not as dangerous. In these horses, the liver is able to “pick up” on the insulin release to produce more glucose for blood circulation to replace the glucose that was impelled into the cells from the protein induced uptake. Mostly, these horses will not exhibit any problems, though many horse owners report that the high protein content make their horses “hot” or more excitable and harder to handle. This is particularly true of horses in stall kept situations or confinement.
My theory is that alfalfa hay is not worth the risk whether the horse is metabolic or not. It is fine as a dietary supplement, but not as their main source of roughage. Many times a caretaker doesn’t know that their horse is metabolic until the horse has a laminitic event, so the risk isn’t worth the chance.