Foraging behaviour,nutrient intake from pasture and performance of free-range growing pigs in relation to feed CP level in two organic cropping systems

In organic pig production one of the major challenges is to be able to fulfil amino acid requirements based on organic and locally grown protein feed crops. The pig is an opportunistic omnivore with a unique capacity for foraging above and below the soil surface. It is hypothesized that direct foraging in the range area can pose an important contribution in terms of fulfilling nutrient requirements of growing pigs. Foraging activity, lucerne nutrient intake and pig performance were investigated in 36 growing pigs, foraging on lucerne or grass and fed either a standard organic pelleted feed mixture (HP: high protein) or a grain mixture containing 48% less CP (LP: low protein) compared with the high protein feed mixture, from an average live weight of 58 kg to 90 kg in a complete block design in three replicates. The pigs were fed 80% of energy recommendations and had access to 4 m² of pasture/pig per day during the 40 days experimental period from September to October 2013. Behavioural observations were carried out 12 times over the entire experimental period. For both crops, LP pigs rooted significantly more compared with HP pigs but the effect of CP level was more pronounced in grass (44% v. 19% of all observations) compared with lucerne (28% v. 16% of all observations). Feed protein level turned out not to have any significant effect on grazing behaviour but pigs foraging on lucerne grazed significantly more than pigs foraging on grass (10% v. 4% of all observations). Daily weight gain and feed conversion ratio were significantly affected by feed protein and forage crop interactions. Compared to HP pigs, LP treated pigs had 33% lower daily weight gain (589 v. 878 g) and 31% poorer feed conversion ratio (3.75 v. 2.59 kg feed/kg weight gain) in grass paddocks, whereas in lucerne paddocks LP pigs only had 18% lower daily weight gain (741 v. 900 g) and a 14% poorer feed conversion ratio (2.95 v. 2.54 kg feed/kg weight gain) compared with HP pigs. LP pigs foraging on lucerne used 169 g less concentrate CP/kg weight gain, compared with HP pigs, indicating the nitrogen efficiency of the system. The results indicate that direct foraging of lucerne may be a valuable strategy in terms of accommodating CP and lysine requirements of organic growing pigs.