Evaluation of dehorning distress and its alleviation in calves : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University
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Date
2002
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Massey University
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Abstract
In this thesis, the pain-induced distress caused by the husbandry practice of dehorning cattle is assessed and methods to alleviate it are evaluated. At the time this work was conducted there were no comprehensive studies on the effects of amputation dehorning upon the welfare of the cattle. The aims of the study were to assess the distress response after dehorning and to explore the possibilities of alleviating that distress through the use of different dehorning tools, local anaesthetic and/or cautery of the scoop wound. Changes in plasma Cortisol concentrations and behaviour were used as indices of distress. It was anticipated that this research would provide scientific data to aid in the writing of welfare codes and advisory material concerning the dehorning of cattle. The Cortisol and behavioural responses of six-month-old male Friesian calves after treatment were studied. In the Cortisol studies, blood samples were taken by venipuncture from the jugular vein of each calf prior to, for the first 9 hours and at 36 h after treatment. Behavioural responses were scored by point scan behaviour sampling for the first 10 h after and on day two between 26 and 29 h after treatment. Amputation dehorning elicited a marked, biphasic Cortisol response that lasted six hours. Dehorning elicited similar Cortisol responses irrespective of the tool employed. ACTH bolus (iv. 0.28μg/kg) elicited a maximal Cortisol response. The similarity of the magnitude of the dehorning and ACTH responses suggests that dehorning was extremely distressing. The plateauing of the plasma Cortisol values between 1.5 and 3 hours after dehorning suggests the appearance of a second phase of pain, presumably from inflammation. Local anaesthesia virtually abolished the first three hours of the Cortisol response after dehorning, after which Cortisol concentrations rose transiently. Overall, this equated to a 50% reduction in the integrated Cortisol response. Cauterizing the scoop wounds effected a marginal reduction in the Cortisol response. The combination of local anaesthesia plus cauterizing the scoop wound virtually abolished the Cortisol response to amputation dehorning. This striking result is reminiscent of pre-emptive analgesia. The destruction of, and the prevention of sensitization of, nociceptors in the wound is thought to contribute to this effect. The four behaviours of tail shaking, head shaking, ear flicking and rumination, met the criteria required to use behaviour as evidence of distress. The interpretation of the behaviour data corresponded with that of the Cortisol data. Taken together, the Cortisol and behaviour data from this study, along with the subsequent work it generated, indicate that scoop dehorning is extremely noxious. If the cattle are older and amputation dehorning is necessary, it is recommended that local anaesthetic be given and if practicable combined with either ketoprofen (McMeekan et al., 1998b) or wound cautery. However, it is preferable to dehorn calves when they are younger by cautery disbudding (Petrie et al., 1996b).
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Dehorning, Veterinary anesthesia, Veterinary anaesthesia