Castration, tail docking and dehorning - What are the constraints?

Castration, tail docking and dehorning - What are the constraints?
Peer reviewed

Abstract

The present public and scientific interest in the welfare of farm livestock has caused traditional management procedures, including castration, tail docking and dehorning, to be scrutinised as causes of stress (stressors). This laudable scientific endeavour is however subject to a range of constraints. Major constraints are the subjective nature of distress, and the consequent difficulty of identifying indices which can be used confidently to quantify it. Nevertheless, behavioural and physiological indices have been identified by comparison with human responses to aversive stimuli, and allow distress to be assessed in animals. Changes in plasma cortisol concentrations, reflecting the activity of the hypothalamic-pituitary-adrenal system, are commonly used as an index of distress in farm livestock exposed to stressors. Judged thus, the distress caused by castration or tail docking of sheep and cattle apparently depends on several factors including the procedure itself, the age of the animal, the method used, the species and possibly the prior method of rearing. Little is known about the distress caused by dehorning of cattle.
Several factors can confound the assessment of distress. They are: (1) balancing the objectivity of the measured indices with subjective judgements about what are acceptable and unacceptable levels of distress; (2) ensuring that the parameters used do indeed reflect distress, and not other phenomena; (3) avoiding erroneous predictions, based on anthropocentric projections and not scientific observations, about expected distress levels in situations which have not yet been examined; and (4) meeting the high cost of rigorous studies in this complex area in which a wide range of factors may affect the outcome. Reducing the distress caused by castration, tail docking or dehorning may be achieved by choosing an age when the distress response is least, choosing the least distressing method, or using anaesthesia (local, general) or systemic analgesia. When a method is identified which causes the least distress, its widespread use on farms should not be recommended unless it is also practicable. To do so will not benefit either the livestock concerned or the industry. Political and trade pressures related to overseas perceptions of New Zealand animal welfare standards require responses based on rigorous scientific assessment. Those responses are likely to involve, as appropriate, vigorous defences of current practices or the adoption of new approaches.

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