Effects of local anaesthesia of 4 to 8 hours duration on the acute cortisol response to scoop dehorning in calves

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Abstract
Objective To determine the effect of a long‐acting local anaesthetic on the plasma cortisol response in calves dehorned using a scoop. Design A physiological study with controls. Procedure Seventy female calves, 3 to 4 months old, were divided into seven groups and dehorned by scoop with or without a long acting local anaesthetic (bupivacaine) which provides local anaesthesia for 3 to 4 h. In some treatment groups the local anaesthetic was given a second time, after 4 h, to give 8 h of anaesthesia. Blood samples were taken before and for 9 h after treatment and plasma cortisol concentrations were measured. Results Scoop dehorning caused a marked rise in plasma cortisol concentration, which returned to pre‐dehorning values after 7 h. The cortisol concentrations of calves given bupiva‐caine were similar to those of control animals for 4 h after dehorning, but then a significant and protracted rise occurred, with concentrations returning to pretreatment values at about 9 h after dehorning. In calves given a second treatment of bupivacaine 4 h after dehorning, the plasma cortisol concentration remained similar to control values for 8 h after dehorning but then increased sharply. Conclusions During its period of activity long‐acting local anaesthetic prevented the rise usually seen after scoop dehorning in plasma cortisol concentrations; by inference it also alleviated the pain‐induced distress caused by this procedure. However, when its effects had worn off the plasma cortisol values rose sharply indicating that animals still experienced pain‐induced distress despite local anaesthetic being administered.