MILK-PRODUCTION FROM GRASS-SILAGE DIETS - STRATEGIES FOR CONCENTRATE ALLOCATION

To investigate strategies for concentrate allocation, 155 multiparous Holstein-Friesian cows received grass silage ad libitum during lactation weeks 4 to 22 in two experiments. A standard concentrate (196 g crude protein (CP) er kg dry matter (DM)) was offered at the same average amount across the lactation period either at a flat rate or as two rates with a change of 6 kg in week 13. Treatments, described as kg concentrate DM per day in the first and second periods of lactation, were 3 : 3, 6 : 0, 3 : 9 (experiment 1), 6 : 6, 9 : 3, 9 : 9 and 12 : 6 (experiments 1 and 2). In experiment 2, two additional treatments maintained CP supply from concentrate after a change from 9 and 12 kg DM by giving 3 and 6 kg high-protein concentrate (HP) DM per day (575 and 383 g CP per kg respectively). Generally as concentrate intake increased silage intake fell, DM intake rose and yields of milk and all milk solids increased linearly. However, in experiment 1 from a base of 3 kg DM, as concentrate intake increased so did fat yield overall and protein yield in mid-lactation but at a declining rate. Fat concentration was depressed at the lowest and highest concentrate levels. Protein concentration rose as concentrate allowance increased particularly at low levels. Increasing concentrate in mid lactation improved protein but not fat concentration. Additional concentrate either spared weight loss or increased weight gain. Distributing move of a fixed allowance of concentrate to early lactation did not affect cow performance overall. Silage intake, milk, protein and lactose yields and protein concentration increased and fat concentration was reduced by giving HP concentrates, effects being greater with 3 than with 6 kg DM per day. Reducing concentrate level while maintaining CP intake did not influence milk and solids yields. The ratios of responses to concentrate CP (3 kg DM per day HP v. 3 kg DM per day standard) compared with concentrate energy (9 kg DM per day standard v. 3 kg DM per day HP) mere 2.1, 2.2, 7.4 and 1.9 for milk, fat, protein and lactose yields respectively Tile results suggest feeding strategies for manipulating the production and quality of milk from grass silage diets.