In a previous short term study, Ferris et al. (1997) demonstrated that similar levels of nutrient intake and animal performance could be obtained by either increasing silage feed value and reducing concentrate feed level, or by reducing silage feed value and increasing concentrate feed level. The principles established in this study were incorporated into this trial to examine two systems of milk production over a full lactation, including both the winter and grazing periods.

Forty high genetic merit dairy cows (PTA95 fat + protein = 38.2 kg), in their second or subsequent lactation, were used in a continuous design full lactation study. Animals had a mean calving date of 1 November and were allocated to one of two systems of milk production, HF or HC, within 36 hours of calving. During the winter, animals on system HF were offered a silage with high feed value characteristics, supplemented with 5.5 kg of concentrate (crude protein concentration of 280 g/kg DM) through an out-of-parlour feeding system.