A poured block reduces feeding associated aggression in sows during gestation

The long-term hierarchical stability of group housed sows can be affected by the method of feeding (Arey and Edwards 1998). Aggression around feeding may lead to detrimental effects on reproductive parameters as a result of the physiological stress response of the sow. Limited opportunity for expression of key behaviours such as foraging and exploration in group feeding systems, heightens competition over access for food. It has been suggested that the behavioural effects of food restriction may be alleviated by providing sows with a substrate (Whittaker et al. 1999). It was hypothesised that the use of a poured block (Sow Enrichment Block, mostly comprised of molasses; Ridley Agriproducts, Pakenham, Vic., Australia) can reduce feeding associated aggression at mixing of sows during gestation.

A commercial gestation diet (14.5 MJ digestible energy (DE)/kg, 0.55 g standardised ileal digestible lysine/MJ DE) was floor-fed at a rate of 2.5 kg/sow/d to all treatments, in a randomised block design study. Groups of 15 multiparous sows were mixed immediately post-mating (d 0) and randomly allocated to one of three treatment groups. The control group was floor-fed once daily; the one block group was floor-fed daily with one 20 kg block placed in the pen (d 0); and the two block group was floor-fed daily with two 20 kg blocks placed within the pen (d 0). Each experimental replicate ran for 4 days and was replicated 10 times with a new group of sows. The measures taken during each 4-day observation period included aggressive behaviour observations (push, chase, attack, bite and threat), recorded for a period of 45 min after feed was presented. Individual sow scratch injuries were counted on a sub sample of sows per pen, on d 1 and 3, as an indicator of aggressive behaviour. The blocks were weighed daily until complete disappearance. Data were analysed using the Univariate GLM procedure (Genstat 15, VSN International, Hemel Hempstead, UK).

Although the presence of the supplement block did not reduce the incidence of fresh scratch injuries when aggressive behaviour is highest on d 1 of mixing sows, injuries were significantly reduced on d 3 (Table 1). This suggests there was a reduction in aggressive interactions as a result of the presence of the block; however, there was no change observed in aggressive behaviours recorded during the 45 min period after feed was presented. Perhaps suggesting aggressive interactions were occurring outside of the time chosen for recording. Block disappearance in groups of sows (P < 0.05) housed with one block was 83 g/sow/d and 75 g/sow/d in groups of sows housed with two blocks. This experiment shows that the provision of a supplement block or blocks reduces the prevalence of fresh scratch injuries by d 3 of mixing unfamiliar sows into group pens.

Table 1.  Mean number of fresh scratch injuries scored on d 1 (day after mixing) and d 3 (3 days post-mixing) of sows in the Control group, One block and Two block and mean time (mins) sows’ spent engaged in aggressive behaviour over the 4-day observation period