Rooting motivation in growing-finishing pigs

Rooting is a strongly motivated, species-specific behaviour of pigs. Most housing systems do not provide appropriate materials that fully allow display of this behaviour. It remains unclear if straw is an appropriate rooting material. We therefore investigated which of the following materials is better suitable to satisfy rooting motivation in pigs: minimal straw, deep straw or compost. Fifty-seven growing-finishing pigs were housed in three pens with one of the three treatments each. Eight pigs per group were individually trained and tested in a conditioned place preference test (CPPT) and another eight pigs in a simple preference test (PT). Stimuli in the tests were either feed freely available (“feed”) or feed hidden in sawdust (“root”). In the CPPT the stimuli were only present during training but not during the test situation. Pigs were tested twice: Once with around 72 kg and once with around 115 kg. A principal component analysis was performed with the variables latency to first decision, first decision, duration spent with each of the stimuli and changes between stimuli. The first two components were then used as outcome variables in linear mixed effect models to assess the effect of treatment, test and session. Results showed that the first two components explained 66.6 % of the variance. The first component (labelled as “rooting preference”) loaded mainly on first decision and duration with the stimuli “feed” and “root”. Pigs housed with compost showed the lowest rooting preference compared to pigs housed with deep straw and minimal straw (treatment: p = 0.06). In the CPPT, pigs housed with minimal straw showed the highest rooting preference compared to pigs housed with compost or deep straw. In the PT, the rooting preference of pigs housed with compost was low, whereas pigs housed with minimal or deep straw showed a higher rooting preference (interaction treatment x test; p = 0.01). The second component (labelled as “hastiness”) loaded mainly on latency to first decision and number of changes, but was not affected by treatment. We concluded that housing with access to compost has a higher potential to satisfy rooting motivation in pigs compared to minimal amounts of straw. Access to deep straw showed intermediate effects.