Effect of Morphine Administration on Social andNon-Social Play Behaviour in Calves.

The objective of this study was to evaluate the effect of morphine on social and non-socialplay behaviour in calves. Twelve calves experienced four treatments in a cross over 2 × 2 factorialdesign: Calves received an intravenous injection of morphine or saline 10 min prior to being testedindividually or in pairs in an arena for 20 min. Play behaviour was continuously recorded in thearena test. Lying times were recorded in the home pen. Cortisol concentrations were measuredbefore and after testing. In the arena test, calves given morphine tended to perform more social playevents than calves given saline, however, morphine administration had no effect on locomotor play.Calves given morphine spent less time lying than calves given saline during the first 4 h afterreturning to the home pen. Cortisol concentrations were suppressed in calves given morphine.Administration of morphine appeared to increase social play but had no effect on locomotor playin calves. This study highlights the importance of investigating different aspects of play behaviourin animals as some may be more indicative of a positive affective state than others. More studiesinvestigating the effects of morphine on play are needed to confirm the results found in this study.