Foraging behaviour of gestating sows on pasture and damages to vegetation cover are influenced by restriction of concentrate feed

One of the main challenges of outdoor pig production systems is their potential environmental impact due to direct deposition of pigs? excreta on the land that can lead to nitrate leaching. However, plants can recycle nutrients, and a sufficient vegetation cover can mitigate adverse environmental impacts of outdoor pigs. The aim of this study was to investigate the impact of concentrate feed restriction on gestating sows foraging behaviour and ensuing damages caused to vegetation cover in a pasture-based system. Ten groups of three sows were randomly assigned to two concentrate feed levels, supplying either 90 % (P90) or 40 % (P40) of metabolizable energy requirements, from week 5 of gestation until farrowing. All groups of sows were housed at a density of 8 sows/ha in a rotational pasture system including a permanent area and three 25 ? 50-m legume-grass pasture plots, which could be accessed in rotation for periods of 2?3 weeks. Posture and location of sows were assessed at weeks 8?9, 12?13 and 15 of gestation using data loggers. During the same weeks, video recordings were made when the sows were at pasture, in order to determine their time spent foraging. Vegetation cover of pasture plots was determined at the beginning and end of the grazing periods using a method based on Unmanned Aerial Vehicle-acquired image processing. In the second half of gestation, P40 sows spent 60 % more time active on pasture than P90 sows during the daytime (P < 0.01). The feeding level did not influence the number of daily visits to pasture plots, but P40 sows spent more time on pasture and travelled longer distances per visit than P90 sows. While at pasture, P90 sows spent more time rooting (P < 0.001) and less time grazing (P = 0.002) than P40 sows. In pasture plots with P90 sows, an increasing proportion of bare soil was observed over time, whereas in P40 plots, a greater proportion of high vegetation was replaced by medium vegetation. These results indicate that a higher concentrate restriction promoted grazing behaviour in pregnant sows, leading to greater disappearance of high vegetation but not to greater vegetation cover destruction. In contrast, the lower concentrate restriction increased the proportion of rooting activity, leading to greater damage to vegetation cover. In conclusion, this study has shown that concentrate feeding level of gestating sows on pasture can be reduced without adverse effects on pasture vegetation cover.

Automated summary

The study investigated the impact of concentrate feed restriction on gestating sows' foraging behavior and vegetation cover. It found that higher concentrate restriction promoted grazing behavior in pregnant sows, leading to disappearance of high vegetation while lower concentrate restriction increased rooting activity, causing greater damage to vegetation cover. Additionally, the study showed that reducing concentrate feed level of gestating sows on pasture did not have adverse effects on pasture vegetation cover.