There are several different types of drugs which can be used to control pain in farm animals. Some are controlled drugs only to be used by a vet due to restrictions under the Veterinary surgeons act. Some methods of pain relief (eg epidural) may be technically difficult and should only to be administered directly by a vet or by a trained technician under direct supervision of a vet. However, It is also recognised that in cases where otherwise an animal may not receive veterinary attention, there is a place for some type of pain relieving medication to be available on farm for the use of a trained stockperson where required.
Currently there are no licensed drugs available for use in sheep. Pain medication which is licensed in cattle or pigs can however be used in sheep at the discretion of the vet. In these cases standard withdrawal periods must be applied to prevent contamination of meat intended for human consumption.
Pain has been defined as an unpleasant, sensory experience representing awareness by the animal of damage or threat to its tissues (although there might not be any damage) that elicits protective actions, and results in learned avoidance. Pain is a complex experience, dependent not only on the severity of the stimulus and the degree of tissue or nerve damage, but also on previous pain experiences.
Pain may be acute, chronic, localised, generalised, physical, emotional, adaptive and maladaptive. An individual may experience several types of pain at the same time. The presence of pain can generally be more reliably identified than the intensity of pain. Pain may also involve fear and lead to the anticipation of more pain causing anxiety – use of electric goads during handling/loading animals would be a good example.
Features of Pain Medication For Sheep
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.