Quantification of the pain and distress responses to castration in young lambs

Pain and distress following castration were assessed in lambs using three indicators: behaviour, plasma cortisol and mechanical nociceptive thresholds. Three castration methods: rubber ring (RR), combined ring and Burdizzo clamp (CM) and surgery (SU) were compared. The effects of castration following local anaesthetic pre-treatment (LA) and castration performed under general anaesthetic (GA) were compared to castration performed with no anaesthetic. This gave a 4 x 3 x 3 block design i.e. 36 experimental treatments. Six lambs were allocated to each treatment i.e. 216 lambs were used in all. SU produced the greatest response, followed by RR then CM castration. LA abolished the responses to RR and CM castration but had no effect on the response to SU castration. GA did not reduce the responses to RR and SU but abolished the rise in mechanical nociceptive thresholds and markedly attenuated active pain behaviours in lambs CM castrated without anaesthesia. This suggests that the clamping procedure itself rather than post-castration pain and distress is responsible for the rise in nociceptive thresholds and active pain behaviours in CM castrated lambs.