Response to the Letter to the Editor on the surgical castration of piglets.

pain relief. In general, anaesthesia does not provide any longterm pain relief. Mischler et al. (1994), however, report a prolonged mild antinociception after CO2-induced anaesthesia. In general, local as well as general anaesthesia should be supplemented with postoperative pain relief. It cannot be concluded from this research that CO2-anaesthesia leads to a mortality of 50%. Based on the results of Svendsen (2006), a pilot safety study was performed. In this pilot it became clear that a safe exposure to 70% CO2 and 30% O2 is time-limited; mortality was deemed unacceptable and thus experiments ended at the death of a maximum of two piglets. Further extensive studies (not published) showed that exposure with a maximum of 2 min is safe. Long-term effects of CO2 inhalation for the given time of 2 min are unlikely to occur in practice. The piglets of the presented research and extensive additional studies did not show any long-term effects; no respiratory diseases or other abnormalities were observed or reported. In conclusion, we agree that anaesthesia and thus CO2anaesthesia will account for a certain amount of stress during induction. It provides, however, an excellent anaesthetic state for a short-lasting surgical procedure such as castration. Additionally, CO2 is an anaesthesia that can be used at a farm level and can easily be integrated in common farm practice, as extensive experience in The Netherlands has shown by now. To complete the improvement of welfare, this anaesthesia should be supplemented with long-term postoperative pain relief. We acknowledge the concerns of the correspondents and thank you for the opportunity to respond to their comments.