Organic growing pigs in pasture systems – effect of feeding strategy and cropping system on foraging activity, nutrient intake from the range area and pig performance. Økologiske slagtesvin på friland – effekt af foderstrategi og afgrødesystem på fourageringsaktivitet, næringsstofindtag fra udearealet samt tilvækst og foderudnyttelse

Summary

Production of organic growing pigs is characterized by indoor housing with access to outdoor concrete yards and feeding high amounts of supplementary feed based on grain and imported protein feed. However, this is not in accordence with the organic principles, which insist on optimization of nutrient recirculation, use of local renewable resources and animals being able to perform normal behaviour.
The overall aim of the project was to contribute to development of an eco-efficent and trustworthy organic production system based on free-range growing pigs in pasture systems. The point of departure was to integrate the unique innate ability of pigs to forage above and below ground as a resource in the farming system. It was hypothesised that foraging in the range area could pose an important contribution to nutrient supply of growing pigs.
Foraging activity, nutrient intake from the range area and pig performance were investigated in 36 growing pigs foraging on alfalfa or grass and fed either a standard organic feed mixture (HP: high protein) or a grain mixture with 52% of crude protein recommendations (LP: low protein) from an average live weight of 58 kg to 90 kg in three replicates. Pigs were fed 80% of energy recommendations and had access to a total of 154 m2 pig-1 during the 40-days experimental period from September to October 2013.
Rooting activity was significantly affected by feed and forage crop interactions but the effect of protein level was more pronounced in grass paddocks with LP pigs rooting 44% of all observations and HP pigs 19% compared to 28 vs. 16% for pigs foraging on alfalfa. Protein level did not have a significant effect on grazing activity but pigs on alfalfa grazed significantly more than pigs on grass (10 vs. 4% of all observations).
Based on crop samples alfalfa intake tended to be significantly affected by protein level with a daily dry matter intake in LP and HP pigs of 470 and 330 g pig-1, corresponding to an energy intake of 0.35 vs. 0.32 Danish Feed Units. Alfalfa crude protein and lysine intake was higher in LP pigs compared to HP pigs but the difference was not significant. Compared to grass paddocks available earthworm crude protein was higher in alfalfa paddocks (84 vs. 55 g pig-1 day-1) indicating the potential of contributing to protein requirements of organic growing pigs.
Daily weight gain and feed conversion ratio were significantly affected by feed and forage crop interactions. LP treated pigs had 33% lower daily weight gain compared to HP pigs (589 vs. 878 g) and 31% poorer feed conversion ratio (3.75 vs. 2.59 kg feed kg-1 weight gain) in grass paddocks, whereas in alfalfa paddocks LP pigs only had 18% lower daily weight gain compared to HP pigs (741 vs. 900 g) and 14% lower feed conversion ratio (2.95 vs. 2.54 kg feed kg-1 weight gain). LP pigs foraging on alfalfa used 169 g less feed crude protein compared to HP pigs, whereas in grass paddocks it was 109 g less, indicating the nitrogen efficiency of the systems.
Regarding development of eco-efficient forage based system for organic growing pigs, further investigations are needed, in particular on suitable forage crops, energy requirements for activity and social interactions and effect of group size on foraging behaviour.