In a 16-week winter feeding experiment, 48 autumn calving cows and heifers were used to compare a control diet, with two diets including fodder beet at a low and a high level. The control diet was ad libitum silage and 6 kg d-1 of concentrates (13.4 MJ (kg DM)-1 of ME and 197 g (kg DM)-1 of CP). The cows offered fodder beet were fed the control diet (C) plus fodder beet at either 2 (L) or 4 (H) kg DM d-1. Soya bean meal was offered with the fodder beet at 0.5 or 1.0 kg d-1 for diets L and H, respectively.

Total dry matter and metabolizable energy intakes were 15.2,16.4 and 17.3 kg DM d-1; 177, 195 and 211 MJ d-1 for treatments C, L and H, respectively. The mean milk yields were not significantly affected by the feeding of fodder beet. There was a significant improvement in the fat and protein content of the milk and yield of constituents. The milk composition and yield of solids were: fat content 42.3,44.2 and 45.9 (s.e.d. 1.25) g kg-1; protein content 33.0, 34.5, 35.3 (s.e.d. 0.76) g kg-1; fat yield 964,1027,1095(s.e.d. 63.2); protein yield 757, 801, 841 (s.e.d. 48.8) for treatments C, L and H, respectively. The treatments had no significant effect on live weight or condition score change.