An Evaluation of Drugs Used in the Control of Stressful Stimuli in Domestic Animals: A Review

There is no universal agreement on what constitutes a stressful stimulus in animals, methods of quantifying the animal response, or the ways by which stress can be ameliorated or prevented. The effect of certain drugs on the clinical, biochemical, hormonal and other changes induced by various stressful stimuli in domestic animals is evaluated. The drugs reviewed include: sedatives that are adrenergic agonists and antagonists (such as xylazine, prazosin and acepromazine) dopamine, benzodiazepines (such as diazepam), opioid agonists (such as morphine), central nervous depressants (such as barbiturates), drugs with hormonal effects (such as metyrapone) and dietary substances (such as magnesium aspartate, tyrosine and ascorbic acid). Most of these drugs are effective, to different degrees, in ameliorating some aspects of the changes induced by the stressful stimuli. Despite their different and often opposing mechanisms of action, they appear to antagonise one or more of the various aspects of the stress response. This is a reflection of the complexity of the stressful responses. The use of drugs to ameliorate or prevent animal stress is ethically important, and may also be of use in improving our understanding of the complex physiological and behavioural aspects of stress. However, from a welfare point of view, the use of vitamins, amino acids and other dietary substances may provide a less expensive, and thus more readily available, alternative to other antistress drugs, if they can be shown to remove or, at least, mitigate a harmful consequence of the stress response. There may be also fewer side effects.