Reducing oral-nasal manipulation in commercially farmed pigs: Fresh wood enhances the efficacy of straw

Lack of suitable materials for rooting and chewing in commercial pig farming has been found to increase harmful behaviours. The aim of this study was to test whether the behavioural benefits of small provisions of straw could be enhanced by the continuous presence of fresh wood. The study was carried out on 167 breeder gilts on a commercial farm in Finland. The pigs were housed in 12-m2 pens with partly slatted floors, six to eight pigs/pen. About 1 litre of straw was given on the floor once a day. The two treatments were: continuous access to either three pieces of fresh birch wood per pen (N=11) or one piece of dried wooden board and one metal feeder chain per pen (N=12). At the age of 4 months, video recordings were made for behavioural analysis. Two periods were observed, totalling 2 hours: before and after distribution of feed and straw. The frequencies of oral-nasal manipulation of conspecifics were analysed with a paired-samples T test (SPSS 21). Receiving straw reduced pig-directed manipulation only in the treatment with fresh wood. Before receiving straw, the mean frequencies of manipulations were 39 events/pig/hour (SD=12) in the pens with fresh wood, and 42 events/pig/hour (SD=12) in the pens with board and chain. After receiving straw, the frequencies were 31 (SD=11) and 41 (SD=9), respectively. The difference between before and after was significant in the pens with fresh wood (t=3.3, P<0.01) but not in pens without (t=0.36, P>0.1). A possible explanation is that fresh wood, but not dry wood and chain, potentiated the effect of a small amount of straw in reducing pig-directed behaviours. It is concluded that in commercial farming, where animals have limited resources, behavioural effects of one resource may depend on the quality of the other resources.