Facial action units, activity and time spent with dam are effective measures of pain in response to mulesing of Merino lambs.

Repeatable measures of pain in ruminants following husbandry procedures are required to validate responses to pain relief. This study tested the hypotheses that facial action units, activity and time spent with dam can be used to assess the efficacy of pain relief in lambs following mulesing. Merino lambs (n = 120) were allocated to one of six treatments implemented at mulesing: (1) lambs that were not mulesed or lambs that were mulesed and administered (2) no pain relief, (3) meloxicam 15 min before mulesing, (4) Tri-Solfen®, (5) a combination of meloxicam 15 min before mulesing and Tri-Solfen after mulesing and (6) meloxicam at mulesing. Facial action units detected a difference in pain between mulesed and non-mulesed lambs at 1 and 5 h post-mulesing (P = 0.005 and <0.001) but not at 26 h post-mulesing. Lambs that were not mulesed were more active and spent more time with their dams than mulesed lambs (P < 0.001). No differences were observed between lambs that were mulesed with or without pain relief. Therefore, facial action units, activity of the lamb and time spent with dam can detect pain in response to mulesing in Merino lambs but cannot detect any changes associated with pain relief.