Do rubber rings coated with lignocaine reduce the pain associated with ring castration of lambs?

To facilitate the wider use of pain relief on-farm, practical 'farmer friendly' methods for administering pain relief are necessary. This proof of concept study evaluated the efficacy of rubber rings coated with local anaesthetic (LA, lignocaine) for providing pain relief in lambs castrated 4 weeks after birth. To eliminate any potential effects of blood sampling on behavioural responses to castration, the study was carried out in two parts, utilising different animals. In the first part of the study, behavioural responses were measured for 60 lambs (n = 10 per treatment) randomly allocated to: (1) handling without castration (C), (2) castration with a normal rubber ring (R), (3) castration with a rubber ring coated with LA (RLA), (4) LA injected into the testes and scrotal neck 4 min before a normal ring was applied (LADR), (5) LA injected immediately prior to a normal ring being applied (LAIR), and (6) injection of LA without castration (IA). Total time lying and frequencies of pain-related behaviour (abnormal lying, activity, postural changes) were recorded by video during baseline (30 min) and 3 h post-treatment. In the second part of the study, cortisol responses were measured for 24 lambs (n = 8 per treatment) allocated to one of three treatments: C, R or RLA as above. Blood samples were taken via jugular venipuncture at 0,30, 60,90 and 120 min and analysed for plasma cortisol concentrations. In the first part, total time spent lying (%) was lower (P<0.01) for RLA and R compared to all other treatments. The frequencies of abnormal lying, activity and postural changes were higher (P<0.05) for RLA and R compared to C and LA. Abnormal lying was less frequent (P<0.05) for RLA (32.6 +/- 3.4 mean +/- SED) compared to R (50.7 +/- 3.4 +/- SED) within the first 20 min post-treatment. However, pain-related behavioural responses of RLA lambs were not reduced enough to achieve best practice levels of pain relief (i.e. IADR). In the second part, cortisol peaked 60 min after treatment for both RLA and R but was lower overall for RLA than R (4473.3 +/- 431.2 vs. 5775.1 +/- 431.2 mean AUC +/- SEM, RLA and R respectively, P<0.05). The lower cortisol and behavioural responses in the RLA lambs relative to R lambs indicate that the lignocaine-coated ring reduced the pain associated with castration to some degree. This technique has potential as a practical method for administering pain relief on-farm. Further development of the rings is required to achieve faster absorption into the tissue and improve pain alleviation. (C) 2014 Elsevier B.V. All rights reserved.