Changes in Forage-Concentrate Ratio of Complete Feeds for Dairy Cows

Two high-forage complete feeds, 95% forage: 5% concentrate and 80% forage: 20% concentrate, each were fed ad libitum to 32 cows from 28 days prepartum to 4 days postpartum. At this time treatments were changed factorially to two higher-concentrate complete feeds, 60% forage:40% concentrate or 40% forage:60% concentrate, for an additional 28 days. Dry-matter intakes and average milk yields following the diet change (days 4 through 32 postpartum) were 14.4 and 23.8 kg/day, 15.2 and 25.1 kg/day, 14.3 and 23.1 kg/day, and 15.4 and 26.0 kg/day for combinations 95% forage to 60%, 95% to 40%, 80% to 60%, and 80% to 40% forage. Volatile fatty acids, pH, and lactic acid were measured in rumen fluid in eight fistulated cows prepartum and on 1st and 8th day after ration change. Molar percentage of acetic acid was lower and molar percentage of propionic acid was higher 8 days after ration change than either prepartum or 1 day after change. Total concentration of volatile fatty acids was higher and pH was lower on 60% concentrate than on 40%. Lactic acid was low (