Multifactorial testing of enrichment criteria: pigs "demand" hygiene and destructibility more than sound

To validate (further) a semantic model called RICHPIG, which was designed to assess enrichment materials for pigs, a study was conducted to examine the importance of three assessment criteria, namely destructibility, hygiene and sound. These material properties were studied using a specially constructed object consisting of a piece of sisal rope, metal wire and three fixed chain links hanging in the pens. The object was considered to be not destructible (ND), hygienic (HY) and not making sound (NS). After a habituation period of 18 h treatments were applied in that the object was (or was not) made destructible with a partial cut in the rope (DE) and/or was soiled with excreta (not hygienic, NH) and/or was allowed to make a tinkling sound by releasing the chain links (SO). The three treatments were applied in a 2 × 2 × 2 factorial design on a commercial farm in seven replicates using seven different units containing eight pens per unit. At five moments in time, ranging from 18 h before until 1 h after treatment, a range of behaviours was recorded including the frequency-related parameter AMI (animal¿material interactions) and four intensity-related parameters. Repeated measures ANOVA's showed significant effects of time and hygiene as well as interactions between time and hygiene, between time and destructibility and between destructibility and sound. Soiling (NH) significantly decreased, and destructibility (DE) significantly increased attractiveness, while sound (SO) was not significant. Only moderate correlations between AMI and the four intensity-related parameters were found (median r = 0.41, all P <0.05), indicating that frequency-related parameters alone may not suffice to determine behavioural importance for animal welfare. This study showed that it is in principle possible to study material properties independent of material type and that it is in principle possible to measure behavioural intensities on a commercial farm. Furthermore, the finding that hygiene and destructibility were more important for pigs than tinkling sounds provided preliminary support for the RICHPIG model.