Some of the challenges in the current practice with sows on pasture and growing pigs housed indoors with access to outdoor concrete areas are the ammonia emissions from the outdoor concrete areas and the high N load on pasture due to the high input of supplementary feed. Furthermore, growing pigs housed indoors does not comply with the organic principles in terms of the possibility to perform species-specific behaviour such as foraging. Alternatively, growing pigs could be integrated into the crop rotation, which would demand a system relying on foraging as much as possible and thus, decrease the input of N in supplementary feed into the system. Based on this, two alternative scenarios with foraging, grass-clover and alternative crops (lucerne and Jerusalem artichokes), respectively, were set up and compared with a scenario resembling the current practice in terms of the environmental consequences of relying on foraging. The indicators representing environmental effects were GHG
emissions and potential N leaching.
The alternative crops scenario showed the best environmental performance with regards to GHG emissions. This was primarily due to the lower import of supplementary feed compared to the other scenarios. On the contrary, estimated potential N leaching was highest in the
alternative crops scenario. Thus, a system integrating foraging of grass-clover, lucerne and
Jerusalem artichokes did not improve the N recirculation at farm level. In the alternative scenarios the input of imported feed was lower than in the scenario representing current practice, which was the rationale behind to introduce foraging. However, the estimated input from biological N fixation of lucerne in the alternative crops scenario was an important contributing factor for the higher N leached.
Based on these results it is relevant to investigate the possibilities to improve the balance between N fixating and non-fixating crops in the crop rotation by introducing other crops with a favourable nutrient composition for pigs, e.g. dandelion, which has a CP and lysine content comparable with lucerne (Jakobsen et al., 2015).
It may also be relevant to combine foraging with other management strategies such as a reduction in supplementary protein feed as a lower N surplus and thereby reduced risk of potential N leaching is related to restricted feeding as found in the study by Eriksen et al. (2006a). A system with growing pigs foraging on lucerne and restricted in protein (107 g CP kg-1 DM feed ~48% reduction) was found to improve the N efficiency of the system by using 169 g less supplementary feed CP kg-1 weight gain compared to a system where pigs were fed according to recommendations (Jakobsen et al., 2015). However, the restricted pigs had a lower daily gain (741 g) compared to non-restricted pigs (900 g) and thus, they have to stay longer in the system before they reach slaughter weight and thus occupy valuable land
resources. The study was based on strip grazing, thus optimizing the availability of forage and reducing pigs’ trampling, which destroys the crop. In practice, the concept of strip grazing has to be developed in terms of technical solutions to decrease the workload related to moving the fences. An additional benefit of strip grazing may be a more even distribution of urine and faeces within paddocks as Stern and Andresen (2003) found that growing pigs given 50 m2 of new pasture each morning, eliminated primarily in that area.
Another strategy to decrease potential N leaching is to reduce the stocking density as reported in Jørgensen et al. (2018). However, combining foraging in the range area with a reduced stocking density may not to be a viable management option as land is a limited resource. Currently, compared to conventional pig production, yields and feed conversion are poorer in organic farming resulting in a higher pressure on land use (van Wagenberg et al., 2017). Hence, preventing N losses is an important prerequisite for increasing yields, thereby improving the production of home-grown crops. In that context, mobile systems may prove useful in distributing the urine and faeces more evenly across the field and by that increase yields as compared to the current practice with nutrient hot-spots exceeding plant nutrient uptake. Furthermore, it is important to identify high yielding crops of a high nutrient value for pigs.
Another possibility may be to combine foraging with seasonal production and include the rooting abilities of pigs to tillage the soil and to forage for root crops and left over crops. In that case, the production of pigs takes place during the growing season with plenty of forage crops and not during winter where the risk of N leaching is high. Also, the capability of pigs for rooting is used as an asset in the system, which would eliminate snout ringing. This demands adaptation of the whole farming systems to this type of production and pigs that are well integrated in the crop rotation. Possibly it needs to be combined with other types of on- farm production and elicit a premium price to make the system economically viable for farmers. Of relevance is also to reduce the input of feed into the system by providing protein according to the pigs’ requirements. Also, it is relevant to reduce feed waste by adequate feed troughs and feed techniques.
In summary
Improved foraging of lucerne, Jerusalem artichokes and grass-clover in the range area turned out to be a feasible strategy in order to reduce GHG emissions but was unsuccessful with regards to reducing estimated potential N leaching compared to current practice. Foraging is an interesting alternative that needs to be developed in terms of technical solutions to allow strip grazing. The system may benefit from implementing the rooting abilities of pigs.
Foraging combined with other production strategies such as seasonal production is suggested to lead to a significant reduction in nitrate leaching.