Duration of action of a topical anaesthetic formulation for pain management of mulesing in sheep.

OBJECTIVE: To investigate the effect of topical anaesthesia on 'mothering up' of lambs after mulesing and marking, and for pain alleviation over a 24-h period.
DESIGN: Two separate trials were performed on Merino lambs undergoing the mules procedure for flystrike prevention, to assess the efficacy of immediate postoperative topical anaesthetic wound dressing containing lignocaine (hydrochloride) 40.6 g/L, bupivacaine (hydrochloride) 4.5 g/L, adrenaline (tartrate) 24.8 mg/L and cetrimide 5.0 g/L in a gel base (Bayer Animal Health, Gordon, NSW, Australia).
METHODS: In both trials, lambs were assigned to one of three treatment regimens: control, mules procedure with topical anaesthetic (0.5 mL/kg) and mules procedure without topical anaesthetic treatment. Parameters measured included body weight, assessment of skin and wound sensitivity to light touch and pain stimulation, behavioural responses and time to mother up and to feed.
RESULTS: In both trials there was rapid (1 min) and prolonged (up to 24 h) wound analgesia as shown by lower scores for light touch (P<0.001) and pain responses (P<0.001), with absent or significantly diminished primary and secondary hyperalgesia (P≤0.05) and significant reduction in pain-related behaviours (P<0.001) in treated versus untreated lambs.
CONCLUSION: Significant pain alleviation and improved recovery can be achieved in lambs for at least 24 h after mulesing through the use of topical anaesthesia. It is suggested that the haemostatic action of adrenalin, together with inhibition of the inflammatory cascade and the barrier effect of the gel within the product, may explain the prolonged anaesthesia up to 24 h observed in the present study. These results suggest that topical anaesthesia has the capacity to dramatically improve the welfare of lambs undergoing mulesing.