Effect of silage:Concentrate ratio on feed intake,growth rate and subsequent milk yield of early calving heifers

The influence of silage:concentrate ratio (energy concentration) on voluntary feed intake, growth rate, feed utilization, reproduction and subsequent milk yield in early calving dairy heifers was examined. Forty-eight heifers of the breed Black and White were divided into four groups fed clover—grass silage and concentrates ad libitum in the ratios 100:0, 75:25, 50:50 and 25:75 of Scandinavian feed units (Sc.f.u.).Below 200 kg liveweight the daily intake of dry matter increased with increasing level of concentrates. Above 200 kg there were no significant differences in dry matter intake. As a consequence of the energy concentration of the rations (70, 78, 89 and 96 Sc.f.u. per 100 kg dry matter), the intake of net energy increased with the amount of concentrates, and consequently the daily gain increased. The increase in daily gain with concentrate level decreased with increasing liveweight.Puberty always occurred at the same liveweight, whereas age at first oestrus decreased with increasing content of concentrates in the ration offered ad libitum. This was reflected in a lowering of the age at first calving from 23.9 to 20.2 months. There was no significant difference in average milk yield in the first lactation. The milk yield was relatively low in all groups, and possible explanations for this depression are discussed.