Physiological and behavioural effects of intradermal injection of sodium lauryl sulfate as an alternative to mulesing in lambs

Objective: To assess the effects on physiology and behaviour of intradermal injection of sodium lauryl sulfate (SLS) as an alternative to mulesing. Procedures: Three groups of Merino lambs were studied: Control (n = 10), SLS (n = 11) and Mulesed (n = 11). The SLS group received SLS (7% w/v) and benzyl alcohol (20 mg/mL) in phosphate buffer, and the Mulesed group received 6 mL topical local anaesthetic as a wound dressing. Haematology, cortisol, beta-endorphin and haptoglobin concentrations, rectal temperatures, body weight and behaviours were monitored for up to 42 days post treatments. Results: SLS treatment induced mild swelling followed by thin scab formation. Fever (>40°C) was observed at 12 and 24 h, cortisol concentration was elevated on days 1 and 2, haptoglobin concentration was highly elevated on days 2-7, white blood cell count was elevated on days 2 and 4 post treatment, but average daily gain was not affected. Fever at 12 h was significantly higher in the SLS than in the Mulesed group, whereas maximum temperature, temperature area under the curve (AUC), occurrence of fever, cortisol profile, cortisol AUC, white blood cell counts and haptoglobin concentrations until day 7 were comparable. The behaviours of normal standing, total standing and total lying were modified for 2 days by SLS treatment, but changes were less marked and of shorter duration than in the Mulesed group. On day 1, the SLS group spent <5% of time in total abnormal behaviours compared with 18% in the Mulesed group. The SLS group tended to spend more time in abnormal behaviours on day 1 than the Controls. Conclusions: The behaviour of the SLS group was similar to that of the unmulesed Controls and their physiological responses were intermediate between the Mulesed lambs receiving post-surgical analgesia and the Controls.