Pigs with but not without access to pieces of recently harvested wood show reduced pen-mate manipulation after provision of feed and straw

In barren environments of commercial farms, pig often redirect their rooting and chewing behaviours at other pigs, which can lead to tail biting. When materials such as straw are provided, the quantity is usually too small to have an effect. The aim of this study was to test whether small provisions of straw and species-relevant point- source objects would have an additive effect in reducing pen-mate manipulation. The animals were 167 gilts with undocked tails on a commercial farm in Finland, housed in 12-m2 pens with partly slatted floors, on average 7 pigs/pen. Liquid feed and 20 g/pig of long straw were provided once a day. The pigs had continuous access to suspended objects: in each control pen (N =12), a 40cm ×10cm ×2 cm piece of commercially sourced wooden board and a 60-cm metal chain, and in each experimental pen (N =12), an 80-cm piece and two 40-cm pieces of birch trees with a diameter of 5–7 cm, harvested 1 month earlier. After 2 months of exposure, frequencies of pig- and object-directed manipulation before and after consuming the feed and straw were recorded by continuous observation on video. Pre-consumption pig-directed manipulation did not differ between the treatments (means: 39.3 events/pig/hour (SD =11.7) in the experimental pens and 42.1 events/pig/hour (SD =12.1) in the control pens; t =-0.6, df =21, P >0.1), but post-consumption manipulation was significantly lower in frequency in the experimental treatment (means: 31.5 events/pig/hour (SD =10.4) in the experimental pens and 41.0 events/ pig/hour (SD =8.6) in the control pens; t =2.4, df =21, P <0.05). Object-directed manipulation was higher in the experimental treatment both pre- and post-consumption (pre-consumption medians: 9.7 events/pig/hour (min =2.0, max =14.9) in the experimental pens and 3.1 events/pig/hour (min =0.9, max =13.7) in the control pens (U =18.5, P <0.01); post-consumption means: 9.2 events/hour/pig (SD =2.7) in the experimental pens and 4.8 events/pig/hour (SD =2.0) in the control pens (t =4.5, df =20, P <0.001). It was concluded that the experimental objects with improved material, quantity, shape and location had an additive effect with straw in reducing pen-mate manipulation, whereas objects ordinarily used on the farm had no beneficial effect. Further research is needed on the effects of the odour, taste and consistency of optimal objects.