Impact of housing on the welfare of the growing pig : what work should be conducted based on current knowledge ?

The effects of housing on the welfare of the growing pig have been investigated through an analysis of the literature. The establishment of the social hierarchy within a group of pigs is achieved through numerous aggressive acts, which are detrimental for welfare (stress, injuries, reduced ADG). Improvements in pen design or environmental enrichment appear to be less effective in limiting the aggression observed when pigs are grouped together, than simply reducing the number of times pigs of different origins are brought together. Limited pen-space per animal lead to more frequent aggressive interactions between pigs and both limited and excessive pen-space lead to a decrease in growth rate. At the present time it is not possible to recommend a minimum pen-space per animal, since group size and floor type also need to be integrated into the estimation. Floor type, as well as the thermal environment, play a role in thermoregulatory activity : this can alter the way different areas are used within the pen over time. For example, the location of the defaecation area could change and this could alter the cleanliness of the pigs. The presence of straw can diversify exploratory activity ; other means of enriching the environment have yet to be developed for other floor types. It is essential to develop and test housing systems before establishing new recommendations. The experiments required to study this subject need to integrate pen-space, group size and feasibility (cost, labour). This importance of environmental consequences should not be forgotten.