The use of analgesic drugs in veterinary practice is increasing, particularly in companion animals. However, farm animals often suffer from conditions (such as foot rot), or are subjected to operations (such as dehorning), which are likely to be painful. Assessment of pain in farm animals can present difficulties and analgesic drugs have not been investigated in any systematic way. Most assessment of analgesic drugs in ruminants has been carried out using experimental models of pain rather than clinical cases. Some indications for analgesics are obvious, such as castration and dehorning. Others are not so obvious, such as mastitis, which is very painful in women, and presumably in cows. Animals in pain are likely to be less productive and there is good evidence that chronic pain will change an animal`s metabolism adversely. Valid reasons for not using analgesics include cost and concerns about residues, which ultimately also means cost. There are several different classes of analgesics, with different attributes. Local anaesthetics are cheap, but short acting. Residues in food have not been an issue in the past, but concerns have been raised in Europe about some metabolites being carcinogenic. Morphine-type drugs are cheap, but less effective in ruminants than other species, are likely to cause residues in food and are strictly controlled by law. Adrenergic alpha-2 agonists are effective, but also cause sedation. Residues can be managed by relatively short withholding times. Probably the most effective analgesics for ruminants are the non-steroidal anti-inflammatory drugs, such as ketoprofen. These have long withholding times for meat, but zero for milk.
Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 359-362, 2002
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