Tail biting is a common problem in modern pig production and has a negative impact on both animal welfare and economic result of the farm. Tail biting risk is increased by management and housing practices that fail to meet the basic needs of pigs. Tail docking is commonly used to reduce the risk of tail biting, but tail docking in itself is a welfare problem, as it causes pain to the pigs, and facilitates suboptimal production methods from a welfare point-of-view. When evaluating the cost and benefit of tail docking, it is important to consider negative impacts of both tail docking and tail biting. Data suggests that tail biting can be managed to an acceptable level even without tail docking, by correcting the production system to better meet the basic needs of the pigs.
Valros and Heinonen Porcine Health Management 2015, 1:2
http://www.porcinehealthmanagement.com/content/pdf/2055-5660-1-2.pdf