1. European Food Safety Authority: Welfare aspects of the castration of piglets. The EFSA Journal. 2004, 91: 1-18.
2. White RG, DeShazer JA, Tressler CJ, Borcher GM, Davey S, Waninge A, Parkhurst AM, Milanuk MJ, Clemens ET: Vocalization and physiological response of pigs during castration with or without a local anesthetic. Journal of Animal Science. 1995, 73: 381-386.
3. Kluivers-Poodt M, Hopster H, Spoolder HAM: Castration under anaesthesia and/or analgesia in commercial pig production. Report. 2007, Wageningen UR, 85, Animal Sciences Group
4. Marx G, Horn T, Thielebein J, Knubel B, von Borell E: Analysis of pain related vocalization in young pigs. Journal of Sound and Vibration. 2003, 266: 687-698. 10.1016/S0022-460X(03)00594-7.
5. Wemelsfelder F, van Putten G: Behaviour as a possible indicator for pain in piglets. Report B-260, Instituut voor Veeteeltkundig Onderzoek 'Schoonoord'. 1985, Zeist, Netherlands