Ask the Vet: Choosing a Muscle Supplement for Your Horse


I’m looking to help my horse build muscle along his topline and hindquarters for show season this year. I’m very confused by all of the different muscle supplements on the market and I’m not sure what is important? What ingredients do you recommend for helping horses to build and maintain muscle? – LP, Illinois

Dear LP,
Healthy muscle development requires both stimulus and building blocks. By “stimulus” I mean exercise or work, and by “building blocks” I mean dietary protein or amino acids. I’ll leave it up to you and your trainer to put together a sound conditioning program for your horse and just speak to the nutritional aspect of your question.

My go-to source for all things equine nutrition is the NRC’s Nutrient Requirements of Horses. This resource says an 1100lb horse in light exercise needs a minimum of 700 grams or about 1.5 pounds of protein per day (forget percentages like 10% and 12%), with 30 grams of that required specifically as lysine, the first “limiting” amino acid.

What does “limiting” mean? According to the NRC, a limiting amino acid is one that, when it is present in less than adequate amounts, will limit protein synthesis. In practical terms, if your horse’s diet is deficient in lysine, he cannot build muscle since this amino acid must be present for any tissue development to take place. A team of researchers conducted an experiment to see if supplementing with lysine (and threonine, the third-most limiting amino acid) would help older horses maintain muscle mass:

Graham-Theirs PM, Kronfeld DS, Hatsell C et al. Amino acid supplementation improves muscle mass in aged horses. J Anim Sci. 2005 Dec;83(12): 2783-2788.

Turns out they got more than they bargained for! The research study showed that horses receiving supplementary amino acids were able to maintain muscle mass better than those without supplementation, regardless of age, as evidenced by improvement in muscle mass scores (and other parameters).

This tells me that providing horses with the first three limiting amino acids—lysine, threonine and methionine—is a smart thing to do if you want to build or maintain muscle. In fact, it probably makes sense to provide all ten of the essential amino acids in the horse: histidine, isoleucine, leucine, valine, lysine, tryptophan, phenylalanine, threonine, methionine, and arginine. “Essential” means the horse requires these ten specific amino acids be provided by the diet, preformed and ready to use. Non-essential amino acids are those the horse can synthesize himself. There are about ten of those, too.

How do you make sure your horse is getting all ten essential amino acids, but especially the most limiting, lysine? While soybean and alfalfa are two examples of high-quality protein sources for horses, bio active whey is actually one of the best sources of protein, with more lysine and other essential amino acids than any common equine feedstuff. So in your particular situation, I recommend you work with your veterinarian and a nutritionist to make sure your horse’s diet is complete and balanced for ALL nutrients, then look for supplements that can be added to ensure adequate levels of protein building blocks are supplied without unbalancing the diet in some other manner. By the way, “high quality” refers to the type, amount, and balance of amino acids in a protein source. The more essential amino acids—especially the limiting ones–the higher the quality. Good luck and have a great next show season!

Lydia Gray, DVM MA, is the Staff Veterinarian for SmartPak. Prior to joining SmartPak, Dr. Gray served as the first-ever Director of Owner Education for the American Association of Equine Practitioners. She has authored numerous articles in publications such as The Horse, Horse Illustrated, Western Horseman and a variety of veterinary journals and magazines. Dr. Gray is also a frequent speaker at horse expos, veterinary conventions and other events. After graduating with honors from the University of Illinois College of Veterinary Medicine and receiving her Master's Degree in Interpersonal and Organizational Communication, she practiced at the Tremont Veterinary Clinic for several years. Dr. Gray is active in the American Veterinary Medical Association and Illinois State Veterinary Medical Association. She enjoys training and showing her Trakehner, Newman, in both combined driving and dressage, and is a USDF “L” Program Graduate (with distinction). Find Dr. Gray on Google+

Posted in Ask the Vet, Weight Management

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