Effects of increasing concentrate energy supply on the performance of loose-housed dairy cows fed grass silage-based diets

Abstract

The effects of increased concentrate level on milk production was assessed during two consecutive indoor feeding seasons according to a continuous randomised block design using 44 (season 1) and 47 (season 2) Finnish Ayrshire cows. Treatments allocated according to a 2×2 factorial design consisted of two concentrate levels and two protein feeding systems. Low and high concentrate feeding regimens were applied to multiparous cows as 9 and 14 kg/day during days 1–150 of lactation and 8 and 11.5 kg for days 151–224, respectively. Primiparous cows received proportionately 0.80 of that fed to multiparous cows. In order to identify the effects of concentrate energy alone, concentrates were formulated so that increases in concentrate feeding resulted in either a constant supply of concentrate crude protein (CP) (mean 1.4 kg/day) or constant intake of rapeseed meal (RSM) (mean 1.7 kg DM/day). Consequently, concentrate CP content decreased with the increasing level of concentrate. Concentrate was offered through computerised self-feeders and silage was fed ad libitum. Increasing energy intake at a constant CP level seemed to have a more negative effect on silage dry matter (DM) intake compared with feeding a constant supply of RSM. Increases in concentrate DM intake resulted in mean substitution rates of 0.48 and 0.25 for CP and RSM diets, respectively. However, the positive effect of concentrate supplementation on milk yield was independent of protein feeding strategies. Milk production increased ( P<0.05) from 24.4 to 26.4 kg energy corrected milk (ECM) when energy level was increased, and on average 0.58 kg milk per kg increase in concentrate DM intake. The response to increased concentrate energy corresponded well with the responses reported earlier with a fixed concentrate composition. It is concluded that it was not possible to compensate a high amount of concentrate with low CP content with low amounts of concentrate with high CP content. However, feed utilization (ECM kg/kg DM) was more efficient for diets containing low amounts of concentrate. The ratio of milk nitrogen/feed nitrogen was highest when a high amount of concentrate with low CP content was used.