Qualitative Behavioural Assessment of Pain in Castrated Lambs

This study investigates for the first time the application of Qualitative Behavioural Assessment (QBA) to the analysis of acute pain expression in castrated lambs, as part of a larger study on the impact of different castration methods on lamb welfare. Eighty 2-day-old male lambs were allocated to one of 4 groups (n=20 per treatment): handled only (control, C), rubber ring castration (RR), short-scrotum castration (SSC) and rubber ring castration combined with Burdizzo (COM). Ethogram-based lamb behaviours and postures were recorded continuously from video for 30 minutes after application of castration rings or handling, and Kruskal-Wallis and Mann-Whitney tests were used to investigate differences between treatment groups. For QBA assessment a 2-minute video clip was extracted from the 30 min footage for each lamb, starting 15 minutes after treatment. Ten observers, blind to the castration treatment, provided QBA of the 80 clips, using Free Choice Profiling methodology. Data were analysed using Generalized Procrustes Analysis. Results show that for the 30 mins after castration or handling RR and SSC lambs had a higher frequency of active pain behaviour (RR=110.5, SSC=97.0, COM=25.0, C=24.0; p<0.001) and restlessness (RR=33.0, SSC=22.0, COM=10.0, C=9.5; p<0.001), than COM and C lambs. QBA identified two main dimensions of lamb expression: ‘calm/comfortable - restless/painful’ (44.8% of variance), and ‘curious/active - tired/lethargic’ (35.8%), with both dimensions showing significant effects of treatment (dimension1: F2,78=13.12, p=0.001; dimension2: F2,78=24.26, p=0.001). Post-hoc analysis showed RR lambs to be perceived as significantly more restless/painful than COM, C, and SSC lambs (T=-6.213, P=0.001; T=-3.805, P=0.001; T=-3.458, P=0.005, respectively), and SSC lambs as more restless/painful than COM lambs (T = -2.8, P=0.03) but not C lambs. In addition RR, COM, and SSC lambs were perceived as more tired/lethargic than C lambs (T=-7.535, P=0.001; T=-7.01, P=0.001; T=-5.904, P=0.001, respectively). In sum, QBA was able to distinguish between four castration techniques through the characterisation of expressive lamb demeanour, with RR castration identified as the most painful. It also characterised COM lambs as more tired/lethargic than Control lambs, where quantitative behaviour measures discerned no difference between the two groups. QBA thus emerges as a promising indicator for the assessment of pain and welfare in castrated lambs.