Nutrient excretion by outdoor pigs: a case study of distribution, utilization and potential for environmental impact

An increasing number of breeding sows is kept outdoors in Europe. Outdoor pig production has benefits in terms of animal welfare but may have hidden costs through nutrient losses. We investigated the distribution of nutrients in sow paddocks and the consequence for losses and utilization in the succeeding crop. Significant correlation between soil inorganic N and the distance to feeding sites was observed after the paddocks had been used by lactating sows fur 6 months (P<0.01). Near to feeders inorganic N levels became extremely high whereas 30-40 m from feeders some patches had N levels in the topsoil corresponding to the levels in the reference area without sows. In the following spring only a minor part of inorganic N was still present in the top 0-40 cm. Similarly, extractable P and exchangeable K in topsoil mere significantly affected by distance to feeders with the highest values close to the feeders (P<0.001). In addition there were significant effects of the distance to huts with increasing nutrient content closer to huts. Although huge variations in dry matter production and nutrient content occurred in the succeeding potato crop, these were only weakly related to the distribution of nutrients (N, P and K) in the previous year, which explained 17% of the total variation in dry matter production. To increase nutrient efficiency in outdoor pig production a uniform distribution of nutrients should be obtained by manipulating the excretory behaviour of the sows and stocking densities must be adjusted to locally acceptable nutrient surpluses.