The influence of chronic pain on the analgesic effects of the α2‐adrenoceptor agonist, xylazine, in sheep

A comparison of the analgesic potency of the alpha 2-adrenoceptor agonist, xylazine, in control healthy sheep and sheep suffering chronic pain from footrot, indicated that the analgesic effectiveness of xylazine was significantly reduced in the animals experiencing chronic pain. This was measured by recording the threshold to a mechanically applied pressure stimulus. Furthermore, when the condition was apparently resolved, by conventional treatment over a period of 2 to 3 weeks, the decreased analgesic effectiveness of the alpha 2-agonist was still apparent although the animals were clinically cured of the footrot.