Tail docking is a husbandry practice widely incorporated in sheep farms around the world. It is an irreversible mutilation that causes severe damage to animal welfare, both immediately and subsequently. Tail docking supposedly contributes to the promotion of local hygiene, which would allow the use of the wool, facilitate reproductive management and reduce the chances of myiasis. However, current understanding of farm animal welfare questions the need to maintain practices such as tail docking. Thus, the aim of this study was to evaluate the effect of tail docking on the incidence of myiasis in sheep from an experimental herd in Brazil in a six-year retrospective cohort.  Relative risk, odds ratio and incidence ratio were the association measures adopted. A total of 4,318 occurrences supplied the analytical model. Tail docking did not decrease the risk and, on the contrary, increased the chances of sheep being affected by myiasis. The results show that the argument that justifies the maintenance of tail docking based on supposed health benefits against myiasis is mistaken.