ABSTRACT
The effects of procaine, mepivacaine and phenylbutazone on pain perception in the equine were studied using two behavioral assays of nociception; the thermal evoked hoof withdrawal reflex and skin twitch reflex. Pain perception threshold was measured as the latency from onset of thermal stimuli to reflex withdrawal of the forelimb or contraction of the cutaneous musculature. Procaine 2% and mepivacaine 2% prolonged the hoof withdrawal reflex latency when administered locally by producing a block of the palmar and metacarpal nerves. Significant analgesia lasted 90 min and 210 min for procaine and mepivacaine, respectively. Phenylbutazone (7.3 mg/kg) failed to alter pain thresholds measured over a 36 h post-treatment period. However, pain thresholds rose over time with successive trials. These data suggest that in the equine (1) phenylbutazone does not alter normal cutaneous pain perception, and (2) successive presentation of painful stimuli increases nociceptive thresholds.
