Use of analgesic drugs for pain management in sheep

Abstract

Awareness of pain and its effects is increasing within the veterinary profession, but pain management in food animals has been neglected. Sheep seldom receive analgesics despite various conditions, husbandry practice and experimental procedures being known to be painful, e.g. footrot, mastitis, vaginal prolapse, castration, vasectomy, penis deviation, and laparoscopy. The evidence supporting use of analgesic drugs in this species is reviewed here. Opioid agonists are of dubious efficacy and are short acting. α₂-agonists such as xylazine are good, short-lived analgesics, but induce hypoxaemia. Non-steroidal anti-inflammatory drugs (NSAID) such as ketoprofen provide long-lasting analgesia, but not as marked as that from α₂-agonists; they should be more widely used for inflammatory pain. Local anaesthetics reliably block pain signals, but may also induce motor blockade. Balanced analgesia using more than one class of drug, such as an α₂ agonist (e.g. medetomidine) and N-methyl-D-aspartate antagonist (e.g. ketamine), with the combination selected for the circumstances, probably provides the best analgesia for severe pain. It should be noted that there are no approved analgesic drugs for use in sheep and therefore the use of such drugs in this species has to be off-label. This information may be useful to veterinary practitioners, biomedical researchers, and regulators in animal welfare to develop rational analgesic regimens which ultimately may improve the health and welfare of sheep in both farming and experimental conditions.

Development of a facial expression scale using footrot and mastitis as models of pain in sheep

“…Reasons commonly cited by veterinarians for not administering analgesia to farm animals include cost to the farmer, withdrawal periods for drug residues and a lack of licensed analgesic products in some animals such as sheep (although they can be used under "The Cascade System") (Lizarraga and Chambers, 2012). One of the major reasons limiting the use of pain relieving drugs in farm animals is difficulties in recognising and quantifying pain (Flecknell, 2008;Huxley and Whay, 2006;Ison and Rutherford, 2014;Lizarraga and Chambers, 2012). There is an evident need for an objective, reliable scoring tool that can be effectively used to recognise and assess pain severity in sheep.…”

Why Pain Is Still a Welfare Issue for Farm Animals, and How Facial Expression Could Be the Answer

“…Commonly reported reasons for not administering analgesia to farm animals include the cost to the farmer, withdrawal periods for drug residues, few licensed analgesics or anesthetics approved for use in production animals, and particular difficulty in recognizing, assessing and evaluating pain [10,60,135]. Becker et al [134], however, found fewer farmers thought it was acceptable to do certain procedures without pain relief when compared to practitioners.…”

“…There are a number of products available to mitigate pain in animals, including local and regional anesthetics, opioids, and non-steroidal anti-inflammatory drugs (NSAIDs); however, in the UK and New Zealand, there is no licensed pain relief product for sheep and any analgesics must be used off-label [10], and up until very recently, in the US there had been no approved pain relief treatments in livestock at all [132,133]. Without access to appropriate anesthesia and analgesia, the use of such products will be limited.…”

“…As a prey species, it is evolutionarily advantageous for farm animals not to overtly express any weakness, and thus one of the most common reasons why farm animals still experience pain is a lack of human ability to recognize it [10]. Effective assessment and alleviation of pain are intrinsically linked, meaning that unless we can recognize it we cannot judge its severity and thus cannot manage it successfully.…”

Palatability of flunixin and pharmacokinetics when administered to sheep through feed

“…Although 51 flunixin has also been shown to be effective for pain relief in sheep (Paull et al 2007; Welsh 52 1995), there are currently no registered NSAIDs in Australia for use in sheep. Pain relief can be 53 logistically difficult and costly to administer to livestock raised in extensive systems due to 54 feasibility of repeated application overtime and availability of registered drugs is limited 55 (Lizarraga & Chambers 2012). A potential practical method of providing pain-relief is through 56 oral administration, allowing farmers to either provide NSAIDs as a drench or through feed in 57 the form of granules or a liquid formulation.…”