It's time for another episode of CH Mythbusters!! Today I want to discuss a myth I hear surprisingly often from those in the saddleseat discipline: "Tail nicking/alteration does not limit my horse's tail movement or at all inhibit him from swishing at flies. It only makes his tail more flexible."
In order to bust this myth, we first have to understand a bit about equine tail anatomy. A horse's tail is comprised of the end of his spinal column, and 3 primary muscle groups: the dorsal sacrocaudal, the ventral sacrocaudal, and the coccygeal muscles. The dorsal and ventral sacrocaudal muscles work together to raise and lower the tail, respectively. The coccygeal muscles are attached to either side of the tail and allow it to be swished back and forth.
Tail nicking/alteration is a practice performed to allow a horse to have the tail pictured above. It rises sharply up from the haunch, then cascades back down. In order to create the level of flexibility necessary for the sharp rise, a veterinarian or trainer (more often a trainer, as the American Veterinary Medical Association is opposed to the practice) will sever the ventral sacrocaudal muscles on the underside of the tail. This allows the tail to be stretched upwards without muscle resistance and placed in a high tail set. This tail set is necessary to prevent the muscles beneath the tail from reattaching.
As the ventral sacrocaudal muscles are completely severed, the horse no longer has the ability to pull his tail down. He can let it drop, but he cannot tuck it or swish it between his hind legs (reducing his ability to ward off flies). As a result, we can clearly see that the claim that tail nicking does not alter a horse's ability to move his tail is false.