Hierarchy positions in groups of sows are settled relatively quickly, though long term stability can be affected by several factors including method of feeding. Fighting is less intense between pigs of unequal sizes, may be reduced by previous exposure but is less affected by the presence of a boar. Larger groups have more hierarchy positions to resolve and therefore more fighting. Greater space allowance appears to have little effect on fighting at mixing but can reduce aggression in the longer term. Barriers can limit aggression by allowing losers to escape more easily. Provision of ad libitum feed has been shown to reduce aggression over the short term. Straw bedding has no effect on fighting. Chemical intervention techniques would appear to delay rather than reduce fighting. Newly mixed sows should be supervised to reduce fighting. The fighting which occurs during mixing results in physiological stress responses which can have detrimental effects on reproductive parameters. However, the short-term nature of this response means that detrimental effects can be avoided by careful timing of regrouping. It is therefore possible to achieve equally good reproductive performance in group-housing systems as in systems with individual housing, provided that good management is practised.

Sandra Edwards