Effects of butorphanol, flunixin, levorphanol, morphine, and xylazine in ponies

The analgesic and behavioral effects of butorphanol (0.22 mg/kg), flunixin (2.2 mg/kg), levorphanol (0.033 mg/kg), morphine (0.66 mg/kg), and xylazine (2.2 mg/kg), given IM were observed in 8 ponies. These ponies were instrumented to measure response objectively to painful superficial and visceral stimuli. Effects on the cardiopulmonary system and rectal temperature also were evaluated in 6 of these ponies. Observations were conducted before drug injection (base-line values) and after injection at 30, 60, 120, 180, and 240 minutes. Xylazine provided the highest pain threshold for the first 60 minutes and a sedative effect for 105 minutes. The effects for superficial pain and visceral pain persisted 3 hours and 4 hours, respectively. Morphine produced good analgesia for superficial pain (30 minutes), whereas butorphanol provided good effect for visceral pain (4 hours). A slight degree of analgesia for visceral pain was obtained after morphine (1 hour) and levorphanol (4 hours); flunixin did not induce analgesia. Butorphanol, levorphanol, and morphine stimulated motor activity. Behavioral effects did not occur after flunixin was given. Xylazine decreased systolic, diastolic, and mean blood pressures. Marked increases in these pressures, heart rate, and respiratory rate were observed after morphine was given. Changes of central venous pressure, rectal temperature, and blood gas values remained within base-line limits after both drugs were given. Butorphanol increased heart rates for 1 hour; flunixin and levorphanol did not alter any of the above values.