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.

In sheep, i.t. administration of ketoprofen and ketamine, alone or together, produced no hypoalgesia; however, they prevented NMDA-induced mechanical hypersensitivity. Ketoprofen and ketamine may have therapeutic potential in conditions associated with persistent pain.

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Pharmacological pain management is necessary under many clinical situations, but in donkeys little information on analgesic drugs is available. This controlled, randomised, crossover, Latin-square, operator-blinded study aimed to assess and compare the hypoalgesic effects of intravenously administered saline and five α2-adrenoceptor agonists on mechanical nociceptive thresholds (MNT) in donkeys. Areas under the threshold change versus time curve values for 0-30, 30-60, 60-90 and 90-120 minutes postdrug administration were used to compare the effect of treatment. As compared with saline, which did not increase MNT, the overall degree of mechanical hypoalgesia induced by xylazine (1.1 mg/kg), detomidine (20 μg/kg), medetomidine (5 μg/kg) and dexmedetomidine (3.5 μg/kg) was limited to 0-60 minutes, and that of romifidine (100 μg/kg) to 0-120 minutes. Although there were no significant differences between the five α2-adrenoceptor agonists during the first 30 minutes postadministration, hypoalgesia induced by xylazine and dexmedetomidine was significantly less intense than that achieved by detomidine and/or romifidine from 30 to 60 minutes. Differences in the overall degree of hypoalgesia induced by each of the α2-adrenoceptor agonists may influence veterinary surgeons towards choosing a particular drug over others for a particular donkey patient.

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Sedation and mechanical hypoalgesia induced by xylazine were enhanced by butorphanol at 40 μg/kg bwt. This drug combination may be suitable for chemical restraint of donkeys undergoing certain clinical procedures.