Three methods of ensiling an alfalfa–bromegrass mixture were compared: field-wilted (W) (45% dry matter (DM)); direct-cut (F) (24% DM) with 85% formic acid added at the harvester at 0.5% w/w; and direct-cut (FF) (25% DM) with a formic acid–formalin mixture similarly added at 0.5% w/w. The formic acid–formalin mixture was a 1:1 ratio of 85% formic acid to 40% formaldehyde. Wilted silage was significantly (P < 0.05) higher in pH and soluble N (percent total N) and lower in gross energy than F or FF. Treatment FF produced significantly (P < 0.05) more total acids, butyric acid, and propionic acid, than did F or W. In a 140-day postparturition dairy trial, 30 Holstein cows were grouped by age and randomly assigned to W, F, and FF silages fed ad libitum. Differences among the mean silage DM intakes of 10.6, 10.6, and 9.8 kg/day and mean solids-corrected milk yields of 23.4, 24.9, and 25.5 kg/day for W, F, and FF, respectively, were nonsignificant (P < 0.05). Fifty-four crossbred beef bulls with an average initial weight of 239 kg were fed W, F, and FF as protein supplements (approximately 2.8 kg DM/day) with high moisture corn ad libitum for 133 days. Mean gains were 1.36, 1.35, and 1.28 kg/day and feed: gain ratios were 5.66, 5.82, and 6.04, respectively, for W, F, and FF. No significant differences (P < 0.05) were found in gains, feed: gain ratios, or carcass composition.