Characterizing neuroma-like formation after tail docking in sheep.

Abstract

Tail docking is a routine husbandry procedure in lambs that causes acute pain. Studies of tail docking performed between 4 and 8 weeks of age have reported neuromas in the tail stump, which are characterized by aberrant nerve proliferation and fibrotic scarring and represent a potential source of chronic pain. However, it remains unclear whether similar lesions develop after rubber ring docking in the first week of life, the age at which this method is commonly recommended. This study examined the histological characteristics of tail stumps in lambs docked with a constrictive rubber ring at 1-2 days of age compared with undocked controls. Eighteen Polypay female lambs (8 docked, 10 undocked) were slaughtered at 7.5 to 8 months of age and their tails collected and decalcified for histology and immunohistochemistry. Tissues were evaluated for abnormalities characteristic of neuromas followed by blinded semi-quantitative scoring of key histologic features. Neuroma-like axon proliferation and fibrosis ranged from mild to severe and were significantly more severe in docked than undocked tails. In addition to neuromatous lesions in the soft tissue, axon proliferation was particularly prominent in the periosteum of the docked vertebral bone. Masson's trichrome staining showed that neural proliferation was accompanied by fibrosis, and immunohistochemistry confirmed that lesions included proliferation of both axons and Schwann cells, characteristic of traumatic neuromas. These findings provide evidence that tail docking with a rubber ring, even when performed at an early age, causes neuroma-like lesions, which may represent a source of chronic pain in sheep.