Lambs were castrated and tail docked using rubber rings and the level of acute pain was assessed using behavioural and physiological methods. Validity was determined by showing how accurately lambs were allocated to their appropriate treatment groups. The treatments were ranked before the experiment according to the amount of tissue damage and its sensitivity to pain (anaesthesia), in decreasing order of severity: 1) castration and tail docking; 2) bilateral castration; 3) unilateral castration; 4) short scrotum castration; 5) short scrotum castration with local anaesthesia; 6) handled. Another group of lambs that been tail docked only acted as a tail docking control for castration and tail docked lambs. Changes in plasma cortisol concentration; 14 postures and 11 active behaviors were recorded for 180 minutes. A principal component analysis (PCA) and discriminant analysis (DA) helped determine the combinations of indices that most accurately allocated lambs to the appropriate treatment groups. Using all individual indices available from the lambs in a PCA, the first two components accounted for 45 % of the variation while use of the DA allocated 79 % of the lambs to their appropriate groups (60 minute data). Values for 30, 90, 120, and 180 minutes were 50, 55, 48, and 48 %, respectively. Simplification of the measurement was carried out by combining indices: total – incidence of active behaviors, relating to movements of limbs, tail and head plus vocalisation; VSS – time spent dog sitting, lying normally with trembling or with partial extension of hind limbs, and statue standing; V4LL – lying with full extension of the hind limbs; AbS – abnormal standing, excluding statue standing. The accuracy of allocation was improved to 60, 79, 71, 64, and 60 % for 30, 60, 90, 120, and 180 minutes using the combined indices. The accuracy for 60 minute data was not improved when increases in plasma cortisol were included. A simplified index consisting of V4LL and REW (movements of tail and limbs) allocated 74 % (60 minute data, 64 % for 30 minute data) correctly. When the treatment groups were combined to represent severe, mild, or moderate pain, the combined indices permitted correct allocation of 91 % and the simplified indices 83 % of lambs to their appropriate groups (60 minute data).