Effects of tail docking and docking length on neuroanatomical changes in healed tail tips of pigs

In pig production, piglets are tail docked at birth in order to prevent tail biting later in life. In order to examine the effects of tail docking and docking length on the formation of neuromas, we used 65 pigs and the following four treatments: intact tails (n = 18); leaving 75% (n = 17); leaving 50% (n = 19); or leaving 25% (n = 11) of the tail length on the pigs. The piglets were docked between day 2 and 4 after birth using a gas-heated apparatus, and were kept under conventional conditions until slaughter at 22 weeks of age, where tails were removed and examined macroscopically and histologically. The tail lengths and diameters differed at slaughter (lengths: 30.6 +/- 0.6; 24.9 +/- 0.4; 19.8 +/- 0.6; 8.7 +/- 0.6 cm; P < 0.001; tail diameter: 0.5 +/- 0.03; 0.8 +/- 0.02; 1.0 +/- 0.03; 1.4 +/- 0.04 cm; P < 0.001, respectively). Docking resulted in a higher proportion of tails with neuromas (64 v. 0%; P < 0.001), number of neuromas per tail (1.0 +/- 0.2 v. 0; P < 0.001) and size of neuromas (1023 +/- 592 v. 0 mu m; P < 0.001). The results show that tail docking piglets using hot-iron cautery causes formation of neuromas in the outermost part of the tail tip. The presence of neuromas might lead to altered nociceptive thresholds, which need to be confirmed in future studies.