Most horse owners appreciate the sight of a well-muscled horse, along with the time and effort riders or trainers must commit to helping that animal fill out. But chances are, fewer owners consider the factors within a horse’s body that allow him to build—or lose—muscle mass.

At the 2013 Alltech Symposium, held May 19-22 in Lexington, Ky., Kristine Urschel, PhD, an assistant professor of equine science at the University of Kentucky, delivered a lecture about muscle metabolism and how equine muscle mass is regulated and reviewed research on the topic.

Skeletal Muscle

Urschel began by describing the basics of equine skeletal muscle and the pathways that regulate muscle mass. Forty to 55% of a horse’s mature body weight is comprised of muscle, she explained. Muscle itself is comprised of roughly 70% water; 20% protein; and 10% fat, vitamins, and minerals, and has both structural and metabolic functions,