Review of literature on the relief of pain in livestock undergoing husbandry procedures

Summary

The objective of this project was to review the current scientific knowledge and literature regarding the relief of pain in livestock undergoing husbandry procedures. A large range of husbandry procedures and recommendations for pain relief are addressed. Pain is a complex phenomenon involving pathophysiological and psychological components that are frequently difficult to recognise and interpret in animals. Pain is an aversive sensory and emotional experience associated with an awareness of damage or threat to the integrity of the animal’s tissues, normally changing its physiology and behaviour to reduce or avoid damage, reducing the likelihood of recurrence and promoting recovery. In the scientific assessment of pain the optimum approach is to select multiple independent measurements. The options include the hypothalamic-pituitary-adrenal axis (cortisol response in most cases), behaviour, immune responsiveness, health and performance.
Pain management aims to alleviate the pain and inflammatory responses following tissue trauma, to improve the animal’s ability to cope with the trauma; and to improve wound healing and help regain normal bodily functions. The absence of pain in the presence of stimuli that would normally be painful is termed “analgesia”. “Anaesthesia” is a term that refers to the loss of sensation, and anaesthetic substances operate by either blocking the nociceptive activity from reaching the brain (e.g., local anaesthesia), or preventing the brain from registering sensations (e.g., general anaesthesia). Analgesic / anaesthetic drugs are usually from the following classes of drugs: opioids; non-steroidal anti-inflammatory drugs (NSAIDs); 2-adrenergic agonists; local anaesthetics; and miscellaneous drugs  e.g., glutamate system antagonists (ketamine). In practice the most useful of these for application to the relief of pain during husbandry procedures include NSAIDs and local anaesthetics, due to their modes of action, administration methods and degree of efficacy.
Routine husbandry procedures in cattle and sheep production include castration, dehorning and spaying in cattle, and castration and tail-docking in sheep. In relation to castration in sheep, rubber rings are the preferred method used by Australian producers (45% of sheep producers). Improvements in pain relief and wellbeing can be achieved by combining rubber ring and clamp castration. Similarly for tail docking, significant improvements in pain relief may be achieved by combining rubber rings with the use of a clamp device. Pain may also be reduced by the use of NSAIDs as analgesic agents during castration and tail-docking. However, there are no NSAIDs registered for use in sheep. In cattle, horn removal is achieved by various methods. Pre-emptive use of NSAIDs is effective at reducing pain but further work is required to optimise the timing of such treatments. For castration of cattle, either closed (burdizzo or rubber ring methods) or open (surgical) approaches are used. Pain relief can be achieved by local anaesthesia (LA), or NSAIDs which have greater effectiveness than the use of LA. Combinations of LA and NSAIDs have shown increased effectiveness of pain relief for many of these procedures. However the need for pre-emptive treatments with NSAIDs up to 20 minutes before the procedure can limit their practical application. Where ovariectomy of heifers is necessary as the only method to control unwanted pregnancies in extensive “range” type beef production, then steps to control mortality due to haemorrhage, and efforts to reduce the associated pain should be used. Immuno-castration as an alternative strategy to spaying and castration in cattle has been developed, but it has practical difficulties that limit its commercial uptake. These difficulties revolve around variability in immune responses and therefore biological efficacy.