EFFECT OF DEHORNING ON BEHAVIOR AND PLASMA-CORTISOL RESPONSES IN YOUNG CALVES

Behavioural and cortisol responses were investigated in respectively 8 4 and 80, 4-8 week old Montbeliard calves. The calves were dehorned ei ther by applying a caustic preparation (potassium hydroxide) at 4 week s or by heat cauterisation at 8 weeks. Behavioural studies, involving 84 calves in four treatments (with and without anaesthesia in dehorned by heat or chemical treatment), were performed by video monitoring or by visual observations. Throughout a 24 h period after disbudding, th e ratio of lying to standing was unchanged in both treatments. The mai n behavioural modifications consisted of drastic but transient reducti on in rubbing and social behaviours concomitant with an increase in be haviours indicative of distress or pain: restlessness (frequent standi ng up and lying down), repeated shaking of the head or ears and scratc hing the lesion with the hind foot. All behaviours indicative of pain or discomfort disappeared within 4 h in both treatments. Cortisol assa ys, performed on 80 calves (different from those used for behavioural studies) showed a peak in plasma cortisol levels (12-18 ng ml(-1)) but this was of moderate magnitude when compared with the 40 ng ml(-1) sh own by three animals in response to an intravenous injection of adreno corticotropic hormone (ACTH). Behavioural changes and plasma cortisol data indicated that calves dehorned without anaesthesia experienced, i n both treatments, intense but brief pain and discomfort. Although the comparison between treatments is questionable because of the differen ces in ages, animals disbudded by heat cauterisation tended to exhibit weaker reactions. Local anaesthesia reduced increases in plasma corti sol in chemically disbudded calves and induced a strong reduction of r eactions in 60% of animals in both treatments. Those results suggest t hat further investigations are required to improve the reliability of a local anaesthetic under practical conditions.