CHANGES IN PLASMA-CORTISOL CONCENTRATION IN LAMBS OF 3 AGES AFTER 3 METHODS OF CASTRATION AND TAIL DOCKING

Lambs were handled only or castrated and tail docked at five, 21 and 4 2 days of age by either surgery, rubber ring or rubber ring and Burdiz zo. Plasma cortisol was measured in blood samples taken before and at 12, 24, 36, 48, 60, 72, 84, 96, 138 and 180 minutes after castration a nd docking. Pre-treatment and peak cortisol values were highest in fiv e-day-old lambs. The peak cortisol values, at each age, were similar f or surgery and rubber ring groups. However, the peak occurred earlier after surgery and rubber ring Burdizzo than after rubber ring only tre atment. The cortisol peak was 28 nmol litre-1 lower after rubber ring Burdizzo than surgery or rubber ring only. Plasma cortisol returned to pretreatment values within 84 minutes after rubber ring Burdizzo, 96 to 138 minutes after rubber ring only but not within 180 minutes after surgery. The changes in plasma cortisol together with the changes in behaviour suggest that the rubber ring Burdizzo method of castration a nd docking of lambs at all ages, was probably the least painful of the methods tested.