64. Stocking density will vary according to the interaction between climate, drainage and stockmanship. Careful judgements must therefore be made to calculate the correct stocking density for a particular site. As a general rule, stocking densities for breeding sows vary between 15-25 sows per hectare (6-10 sows per acre) but it is necessary to set the level to match the quality of the site. Ideally, 4-6 hectares (10-15 acres) of clean ground per 100 sows should be available each year, with the ground clear of pigs for at least six months between batches. It is important for the pig-keeper to make a careful assessment of the ground conditions on a new site before setting a stocking density and we would encourage a low stocking density initially, with the option of increasing stocking density in the light of experience.
65. Whilst we suggest an overall stocking density of 15-25 sows per hectare, we recognise that the density within each paddock can be higher than this. For example, in a recent survey of management and welfare in outdoor pig production systems, it was stated that average stocking densities in service, dry sow and farrowing paddocks can be 33, 27 and 19 pigs per hectare respectively (reference: Abbott, T A, Hunter, E J, and Guise, H J (1994) Survey of management and welfare in outdoor pig production systems in "Welfare of Extensively Farmed Animals", Scottish Centre for Animal Welfare Sciences, Edinburgh, 3 September 1994).