Behavioural traits of undocked heavy pigs receiving different enrichment tools

The aim of the present work was to investigate the effects of innovative enrichment devices on the behavioural traits of undocked Italian heavy pigs kept on slatted floor in the body weight range 25-160 kg. Two separate and independent trials (n=40 pigs each, 5 pigs/pen) were carried out. In Trial 1, 20 pigs received a hanging metal chain (C1, positive control) as environmental enrichment, and 20 received wood logs (WL) placed inside a specifically designed metal rack allowing snout and biting manipulation. In Trial 2, 20 pigs received a metal chain (C2, positive control) whereas 20 received a specifically formulated vegetable edible block (EB) placed inside the same metal rack. The manipulable materials were always available to animals. Pigs were videotaped every 2 weeks and behaviour was analyzed by the same trained observer (scan-sampling for general behavior and all-occurrences sampling on three selected days for the number and the duration of the interactions with the devices). Data were submitted to one-way ANOVA (using the pig as the experimental unit and the environmental enrichment as the main effect). Kruskal-Wallis test was used for non-parametric data. General behavior was only marginally affected by all enrichment tools, although EB pigs spent less time in (aimless) rooting/exploring the pen floor (13.39 vs. 15.90% of the observed behaviours, P<0.01) than C2. In Trial 1, WL pigs interacted with the enrichment tool less than C1 pigs (0.64 vs. 1.84%, P<0.01). In Trial 2, EB pigs interacted more with the enrichment (2.85 vs. 1.12%, P<0.001) if compared to C2 group. These data were confirmed by in-continuous observation. In conclusion, our results show that edible blocks (EB) but not wood logs (WL) were more attractive for pigs than hanging metal chains (C1 and C2). The research was funded by Progetto AGER, grant n°2011-0280.