The AVMA endorses the American Association of Equine Practitioners’ (AAEP) policy on "Tail Alteration in Horses," which reads as follows:
“The American Association of Equine Practitioners condemns to the alteration of the tail of the horse for cosmetic or competitive purposes. This includes, but is not limited to, docking, nicking (i.e., cutting) and blocking. When performed for cosmetic purposes, these procedures do not contribute to the health or welfare of the horse and are primarily used for gain in the show ring (nicking/cutting, blocking and docking) or because of historical custom (docking). If a horse’s tail becomes injured or diseased and requires medical or surgical intervention, such care should be provided by a licensed veterinarian.
The AAEP urges all breed associations and disciplines to establish and enforce guidelines to eliminate these practices and to educate their membership on the horse health risks they may create. Members of AAEP should educate their clients about the potential health risks, welfare concerns, and legal and/or regulatory ramifications regarding these procedures based on the relevant jurisdiction and/or association rules.”
Welfare Implications of Horse Tail Modifications (PDF)