The effect on dairy cow performance of adding molassed sugar beet feed to immature forage maize at ensiling or prior to feeding

Twenty-four Holstein Friesian cows were assigned in groups of six cows to four dietary treatments according to a 4 × 4 Latin square design, providing a cross-over experiment lasting 16 weeks. All cows received 1 kg/day extracted soya bean meal and 5 kg/day of a standard dairy concentrate. The four treatments were: ad libitum high quality (dry matter (DM) 360 g/kg, metabolisable energy (ME) 11.0 MJ/kg DM) grass silage (GS), or a fixed amount of grass silage (4.4 kg DM/day) plus either ad libitum amounts of an immature maize silage (DM 201 g/kg, M), the maize ensiled with molassed sugar beet (MSBF) feed (EMS) or the maize silage mixed with MSBF just prior to feeding (MMS). Total forage intake was lower for treatment M than for the other treatments (P<0.05). Yields (kg/day) of milk (P<0.05), butterfat and protein (both P<0.001) were higher for diet EMS than for GS or M but were not significantly different (P>0.05) to the values obtained for diet MMS (values were: yield 24.7, 24.3, 23.2, 23.1; butterfat 1.091, 1.070, 0.998, 0.999; protein 0.849, 0.823, 0.780, 0.758 for EMS, MMS, GS and M, respectively). Milk protein concentration was lower (P<0.001) for cows receiving diet M than for the other diets. Replacing approximately two-thirds of a high quality grass silage by a low DM maize silage without addition of MSBF reduced forage DM intake but had no effect on output of milk, fat or protein. Replacement of grass silage with maize silage with added MSBF (diets EMS and MMS) led to increases in milk fat and protein yield. There was no beneficial effect of ensiling maize with MSBF compared to including MSBF in the diet immediately prior to feeding.