Abstract
Simple SummaryPlay can be used as an indicator of welfare in animals, because animals play more when all their basic needs are met. Opioids have a modulatory effect on social play behaviour in rodents and primates, however little is known regarding the central mechanisms involved in play behaviour in ruminants. In ruminants, we need to know more about what factors influence play behaviour, to determine which elements of play may more accurately be used as indicators of positive welfare. Therefore, the objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. In an arena test, morphine administration increased the performance of social play events but had no effect on locomotor play in calves. Similar to research in rodents and primates, morphine administration appears to increase social but not non-social elements of play in calves, suggesting that increased social play may be more indicative of a positive affective state.The objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. Twelve calves experienced four treatments in a cross over 2 × 2 factorial design: Calves received an intravenous injection of morphine or saline 10 min prior to being tested individually or in pairs in an arena for 20 min. Play behaviour was continuously recorded in the arena test. Lying times were recorded in the home pen. Cortisol concentrations were measured before and after testing. In the arena test, calves given morphine tended to perform more social play events 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 after returning 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 play in calves. This study highlights the importance of investigating different aspects of play behaviour in animals as some may be more indicative of a positive affective state than others. More studies investigating the effects of morphine on play are needed to confirm the results found in this study.
Highlights
Play behaviour in calves is reduced when conditions are suboptimal, such as in response to low milk allowance, weaning [1] and after dehorning [2]
Because play is reduced when animals are exposed to negative stimuli or environmental challenges, play has been identified as a potential indicator of welfare in animals [3]
Play could potentially be used as an indicator of good welfare
Summary
Play behaviour in calves is reduced when conditions are suboptimal, such as in response to low milk allowance, weaning [1] and after dehorning [2]. Because play is reduced when animals are exposed to negative stimuli or environmental challenges, play has been identified as a potential indicator of welfare in animals [3]. In particular social play, is a pleasurable and Animals 2019, 9, 56; doi:10.3390/ani9020056 www.mdpi.com/journal/animals. Play serves an important biological function through shaping the development of behavioural flexibility as well as appropriate social and cognitive behaviours [6]. Play could potentially be used as an indicator of good welfare. It is widely accepted that it is important that animals do not suffer, but that they have the opportunity to experience positive emotional states [7]. In order to ensure good animal welfare, we need to be able to assess positive experiences in animals
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