MILK-PRODUCTION FROM GRASS-SILAGE DIETS - EFFECTS OF SILAGE CHARACTERISTICS AND THE AMOUNT OF SUPPLEMENTARY CONCENTRATE

High digestibility ryegrass was ensiled using either good methods incl uding formic acid application (HDG) or poor methods without formic aci d (HDP). Low digestibility ryegrass (LDG) and lucerne (LUC) were ensil ed using similar methods to HDG. Digestible organic matter in the dry matter (DM) in vivo (DOMD) for HDG, HDP, LDG and LUC were 0.756, 0.774 , 0.645 and 0.562 respectively. Silages were offered ad libitum to 40 Holstein-Friesian cows in two Latin-square design experiments during w eeks 8 to 22 of lactation either alone (experiment 1) or with 3, 6, 9 or 12 kg concentrate DM per day (experiment 2). Relative intakes of si lage given alone were respectively 1.00, 0.44, 0.98 and 0.79. Low inta ke of HDP could not be predicted from silage analysis. In experiment 2 , DM intake increased by 0.11 kg and milk yield by 0.24 kg for each 0. 010 change in grass silage DOMD. Intake of HDG, LDG and LUC declined l inearly with increasing concentrate, on HDP the effect was non-linear and intake increased up to the 6 kg level. In experiment 1, milk and p rotein yields were greatest on HDG, protein yield was higher on LDG th an LUC and fat concentration higher on HDP and LUC. With supplementati on milk yield was greatest on HDG up to the 6 kg level, at higher leve ls differences between silages were not significant. Fat concentration was highest on LDG and protein highest on HDG and lowest on LUC. On a ll silages giving the highest concentrate level reduced the concentrat ion and yield of fat. Protein concentration increased up to the 9 kg l evel. Fat plus protein yields reached a maximum on HDG with 6 kg conce ntrate DM per day and with 9 kg on the remaining silages.