Banned in several European countries, as well as three US states, and opposed and criticized by the American Veterinary Medical Association, Canadian Veterinary Medical Association, experts, scientists, and representatives of industry, tail docking of cows in the dairy industry—the partial amputation of up to two-thirds of the tail, typically performed without anesthetic—is still permitted in most of the United States. Scientific studies have shown the practice to cause serious welfare problems for animals, including distress, pain, and increased fly attacks.
The Humane Society of the United States, "An HSUS Report: Welfare Issues with Tail Docking of Cows in the Dairy Industry" (2012). IIA. 19.