The “Fly Twitcher” muscles
🦟 Since it’s officially fly season let’s talk about the “fly twitcher” muscles formally known as the cutaneous muscles!
I’m sure you’ve seen and wondered what those lines are across your horses trunk or shoulder?
Those happen to be the most superficial layer of muscle of the horse. The cutaneous group consists of the cutaneous trunci, cutaneous omobrachialis, cutaneous colli, and cutaneous fasciae. The cutaneous trunci which covers much of the trunk is the one people are probably most familiar with. It’s thickest portion sits directly under the saddle girth and it has a visible ridge near the flank in quite a few horses. The role of these muscles is essentially to twitch the skin in response to stimuli in order to remove irritants like flies; this is known as the panniculus reflex. These muscles vary in size from horse to horse and sometimes can be quite visible making distinctive “lines”.
What causes these lines to be so visible on some horses?
—Occasionally these muscles can be recruited to assist when there is a primary weakness or dysfunction. Cutaneous omobrachialis can assist in shoulder function and cutaneous trunci can assist in drawing the hind leg forward and stabilizing the trunk.
—It may be hypertrophic because of an active fly season or a sensitive horse and these lines will come and go.
—Personal signature - all horses are different and unique and sometimes they are just more visible on certain horses in the absence of pathology.