Effects of Tail Docking in sheep on histological features of the muscles of the pelvic diaphragm

Tail docking in sheep husbandry is often performed due to tradition rather than necessity. This practice causes mild to moderate acute pain and the magnitude of the pain associated with tail removal seems to be related to length of tail removed. Ultra-short docking increases the risk of rectal and vaginal prolapse at lambing relative to sheep with longer tails and predisposes to neuroma and nerve degeneration. The aim of the present study was to evaluate the histological features of the muscles and the related nerves of the pelvic diaphragm in adult sheep subjected in the past to caudectomy as well as in intact lambs. After euthanasia, small samples of external anal sphincter, levator ani, coccygeal muscles and branches of deep perineal nerve were obtained, processed according to the usual histological techniques and stained with hematoxylin-eosin and Masson's trichrome. The results showed changes in shape and size of the muscle fibers of the adult sheep. In fact, enlarged or “moth-eaten” fibers were observed amidst normal sized fibers in each of the three muscles of the pelvic diaphragm; furthermore, some internal nuclei were observed. On the contrary, the lambs’ muscles appeared normal. Conversely, the nerve fibers were found to be normal both in sheep and lambs. The muscle abnormalities observed in tail-docked sheep suggest that caudectomy, in the long term, may predispose to prolapses. Improved understanding of the long-term consequences of tail docking, especially the possibility of chronic pain, is needed.