Investigating the reward cycle for play in young pigs

Sammanfattning: A reward cycle for investigating the emotional status in animals has been developed and it requires that animals go through three main phases, i.e. anticipation, consumption and relaxation. The reward cycle has not been tested previously for access to play in pigs. Therefore, the aim of this Master thesis was to investigate if growing pigs showed more behaviours indicative of excitement than pigs that were not allowed to play, performed play in a play arena and showed more behaviours indicative of relaxation after play when they were back to their home pen than pigs that were in their home pen the whole time. Forty undocked piglets (10 litters of Specific Pathogen Free half pure-bred Yorkshire and half hybrids of Yorkshire x Landrace balanced for breed between two treatments were used. From 44 days of age the selected pigs were housed in a weaner stable with four per pen, two castrated males and two females with the most average weights, in their original litter in pens with a size of 6.5 m2 called “home pen”. Within each litter two non-play and two play pigs were randomly selected. Focal animals were individually marked by pig marking spray. After five days of acclimatization to the new environment, four days of training started during which two pigs were allowed to walk to the holding pen (2.0 m2) where they were kept for three minutes. After that the mesh gate opened and the pigs walked in freely to the play arena (5.8 m2) where they stayed for 15 minutes. Two of each of the following objects were used as toys in the play arena: wellingtons, brush, traffic cone, rubber pipe, ball and knotted rope. Half of the piglets had previous experience of objects (i.e. knotted rope, ball and tire) around weaning. Play pigs were observed (instantaneously at 30 s intervals and continuously within each 30 s) 3 min. in the holding pen and 15 min. in the play arena. Non-play pigs were only taken to the holding pen (3 min.) and brought back to their home pen. Play pigs were directly after coming back to the home pen observed for 10 min. and non-play pigs were observed on days without play sessions for 10 min. Statistical analysis was done with Generalized Linear Model for Mixed procedures that tested effect of treatment, time, week, sex and previous toy experience. In the holding pen play pigs performed significantly more locomotor play (P<0.01), play fight (P<0.05), elimination (P<0.01) and had more curled tail position (P<0.01) than non-play pigs. However, non-play pigs performed significantly more explore bar than play pigs (P<0.05) in the holding pen. Pigs of both treatments were numerically more often recorded in zone 1 and orient 1 (i.e. closest proximity to the play arena). In the play arena object play was the most performed play type and then locomotor play which both decreased over time (P<0.001). Social play was the least performed play behaviour but even if it stayed close to zero it showed a slight gradual increase over time (P<0.001). Thus, as predicted they performed all three types of play. The most and the least preferred toys were numerically the brush and the ball respectively. In the home pen play pigs performed significantly more social contact (P<0.001), moving (P<0.001) and exploring (P<0.001), a tendency for drinking more (P<0.1) and significantly less locomotor play (P<0.05) than non-play pigs. In the home pen, non-play pigs performed significantly more lying (P<0.001) and had the tail in a hanging position more (P<0.001). Those behaviours expected to be relaxation-related, such as drinking, eating and rubbing against pen structures, were not significantly higher in play pigs. In conclusion, play pigs showed some behaviours indicative of anticipation in the holding pen, they performed all three types of play in the play arena. However, play pigs did not show behaviours expected to indicate relaxation in the home pen.