EFFECTS OF LOCAL-ANESTHESIA OF 4 TO 8 HOURS DURATION ON THE ACUTE CORTISOL RESPONSE TO SCOOP DEHORNING IN CALVES

Objective To determine the effect of a long-acting local anaesthetic o n the plasma cortisol response in calves dehorned using a scoop. Desig n A physiological study with controls. Procedure Seventy female calves , 3 to 4 months old, were divided into seven groups and dehorned by sc oop with or without a long acting local anaesthetic (bupivacaine) whic h provides local anaesthesia for 3 to 4 h. In some treatment groups th e 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 treatm ent and plasma cortisol concentrations were measured. Results Scoop de horning caused a marked rise in plasma cortisol concentration, which r eturned to pre-dehorning values after 7 h. The cortisol concentrations of calves given bupivacaine were similar to those of control animals for 4 h after dehorning, but then a significant and protracted rise oc curred, 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 simil ar to control values for 8 h after dehorning but then increased sharpl y. Conclusions During its period of activity long-acting local anaesth etic prevented the rise usually seen after scoop dehorning in plasma c ortisol concentrations; by inference it also alleviated the pain-induc ed distress caused by this procedure. However, when its effects had wo rn off the plasma cortisol values rose sharply indicating that animals still experienced pain-induced distress despite local anaesthetic bei ng administered.