Influence of access to grass silage on the welfare of sows introduced to a large dynamic group

This experiment investigated the effects of providing access to grass silage on the welfare of sows introduced to a large dynamic group. Two treatments were applied: (1) access to racks containing grass silage (offering an average of 1.9 kg silage/sow/day), and (2) control treatment with no grass silage racks. Treatments 1 and 2 were applied to two separate dynamic groups, each containing 37 (2) sows. Approximately 9 sows were replaced in both groups at 3-week intervals, and each of these replacements constituted a replicate of the study. The study was replicated six times using a total of 108 sows. In a time-based cross-over design, treatments were swapped between the two dynamic groups after three replicates. Highest levels of rack usage were shown between 08:00 and 14:00 h. During peak periods, 9.8% of sows were observed at the racks at a given time. On average, 78.5% of sows observed at the racks were newly-introduced animals. Overall levels of aggression to which newly-introduced sows were exposed on the day of introduction to the group were low, and did not differ significantly between treatments (P > 0.05). In addition, injury levels measured 1-week post-introduction to the group did not differ significantly between treatments (P > 0.05). Sham chewing behaviour was more prevalent in the post-rather than the pre-feeding yard (P < 0.05), and was significantly reduced in both resident and newly-introduced sows when silage was provided (P < 0.05). Newly-introduced sows in the silage treatment also spent more time lying in kennel areas and less time lying in slatted areas than sows in the control treatment (P < 0.05). In addition, newly-introduced sows in the silage treatment spent less time performing exploratory behaviour within kennel areas than sows in the control treatment (P < 0.05). The results of the present study suggest that the welfare of newly-introduced sows to dynamic groups is improved by provision of access to grass silage. This was reflected in reduced sham chewing behaviour, and increased use of kennel areas for lying behaviour. (C) 2006 Elsevier B.V. All rights reserved.