Shock-elicited flight response in chickens as an index of morphine analgesia

Morphine influence on a flight response elicited by wing shock was examined in 17-day-old chickens. The chickens received either morphine (30 mg/kg) or saline on two days and were tested for responsivity to wing shock 30 min after each injection. On a third day all chickens received saline injections and were tested again. Tests consisted of delivering wing shock at increasing intensity to determine the threshold of a species-typical flight response. Morphine significantly increased the flight response threshold on the first test (analgesia), but not on the second test. Shock intensity values required to elicit the flight response in morphine and saline groups did not differ significantly on the third test when all birds received saline. In contrast to previous evidence, these results demonstrate morphine analgesia in chickens using a dose that approximates the analgesic dose range reported for other species.