An equine model, subjected to three kinds of
pain (superficial, deep, and visceral) was used to test effects of
analgesic drugs. Two groups of ponies were used. In the first group of six ponies, six drugs (
fentanyl,
meperidine,
methadone,
oxymorphone,
pentazocine, and
xylazine) were given according to a Latin square experimental design, and tests were made at 30-minute intervals for 4 hours. Mean values (control) for the three kinds of
pain were obtained before and after the tests and were compared with the mean values (drugs) obtained over 2- and 4-hour intervals (four and eight measurements per interval, respectively).
Xylazine was significantly more effective in obtunding deep
pain (P less than 0.05) at 2- and 4-hour intervals than were the other drugs. Significant differences were not found between values for controls and values for drugs tested for relief of superficial and
visceral pain at 2- and 4-hour intervals. In the second group of four ponies, the
drug (
xylazine) determined most effective in group 1 ponies was given alone or in combination with the next most effective drugs (
fentanyl,
meperidine, and
oxymorphone). Data were obtained in the same manner as for the first group. Mean values were calculated for 2- and 4-hour intervals, and the variance was analyzed.
Xylazine and
fentanyl combined had the best 2- and 4-hour performance for the relief of
visceral pain in the second group (P less than 0.1). Neither
xylazine nor a combination of drugs differed markedly from control values for 2- and 4-hour intervals for relief of superficial and deep
pain.