Effects of silage made from primary or regrowth grass and protein supplementation on dairy cow performance

The effects of protein supplementation on silages made either from primary or regrowth grass (Phleum pratense-Festuca pratensis) and interaction effects between the silage type and protein supplementation were studied in an experiment with dairy cows. The silages were fed ad libitum and supplemented with concentrates (11 kg/day) containing different proportions of grain and rapeseed cake (RSC) R0 (100/0), R1 (890/110), R2 (780/220) and R3 (670/330), and having different crude protein (CP) contents (g/kg DM) 138 (R0), 162 (R1), 186 (R2) and 211 (R3). A cyclic cross-over design experiment was conducted with 16 cows, 8 diets and 4 periods. The silage made from primary grass (PG) had higher energy (11.3 vs. 10.0 ME) and CP (234 vs. 156 g/kg DM) contents compared to silage made from regrowth grass (RG). On PG diets the cows consumed 1.4 kg DM more silage and produced 2.4 kg more milk and 94 g more milk protein than cows on RG diets, but utilization of energy and absorbed amino acids (AA) was lower (P < 0.001) compared to those on RG diets. Increased RSC content in the diets increased the intake of silage (from 9.4 to 10.7 kg DM) and absorbed AA (from 1748 to 2051 g) and the milk yield (2.3 kg, P < 0.01) linearly. Concerning the energy-corrected milk (ECM) yield, there was a linear effect (P < 0.001), a tendency to a quadratic effect (P = 0.09) and a cubic effect (P < 0.05). In the protein yield there were both linear (P < 0.001) and quadratic (P < 0.05) effects. Utilization of CP decreased linearly (P < 0.001). There was a significant interaction effect on energy utilization (P = 0.035), because when the two highest levels of RSC were included in the PG diets, the energy utilization decreased. There was no interaction effect on the utilization of absorbed AA.