The promotion of play behaviour in grow-finish pigs: the relationship between behaviours indicating positive experience and physiological measures

The provision of opportunities to express rewarding behaviours is a promising concept to support a better quality of life for intensively farmed pigs. Play behaviour has been associated with excitement and fun, suggesting that playing animals experience pleasurable states. Pigs play intensively between 2 to 6 weeks of age and this decreases with age thereafter. To determine if the provision of play opportunities could enhance the quality of life of pigs, this study investigated if play can be promoted and sustained in pigs beyond the natural period of expression in a commercial setting. Whether play is positive for pigs and the effect of play on average daily gain and stress physiology was also explored. Growing pigs (n = 288, 10 weeks of age), housed in standard partly-slatted pens, were assigned to either a Control treatment with no play interventions (CON, 1 m2/pig); or to a Novelty (NOV) or Play pen (PLP) treatment, with play promotion between 10 to 21 weeks delivered through play sessions 3x/week. Play treatments received the intermittent provision of destructible novel objects provided either in the home pen (NOV, 1 m2/pig), or in an enclosed ‘play pen' area providing extra space (PLP, 2.9 m2/pig). To understand if play is positive, the frequency and duration of anticipatory behaviour were recorded before play sessions, whilst play behaviour, along with indicators of emotional valence such as vocalization, tail, and ear postures, were recorded during play sessions on focal pigs (n = 144) at 11, 16 and 21 weeks. To explore the physiological response to play, saliva was collected pre and post play, and analysed for cortisol and alpha-amylase, and growth rate was calculated from trial entry and exit weights. Pigs in PLP and NOV played more frequently (p = 0.002) and for a longer duration of time (p < 0.001) across weeks compared to CON. NOV and PLP did not differ in play frequency and duration, except for week 21 when PLP played more frequently. Play treatments expressed more anticipatory behaviour and behavioural indicators associated with a positive experience (ears relaxed and forward, tail wagging, barks) compared to CON. Cortisol was elevated only in NOV compared to CON after the play session, but alpha-amylase and growth rate did not differ. Play was successfully promoted and sustained until the finishing period and equally expressed regardless of extra space. Pigs with play opportunities expressed indicators that play is a rewarding and motivating behaviour and could enhance the quality of life of farmed pigs when supported.