Abstract

Thirty cows (9 uniparous and 21 multiparous) were fed three diets during weeks 5–16 of lactation. The dietary ingredients were adjusted weekly to reflect their oven dry matter (DM). The control diet was a low-fiber diet containing urea-treated corn silage (UCS), well-dried alfalfa hay and buffered concentrate (525:125:350 DM basis). The two test diets contained corn silage and either wilted-alfalfa silage (WAS) or alfalfa hay treated with propionic acid (PAH) and concentrate (300:300:400 DM basis). For the three blended diets, acid detergent fiber (169, 195 and 212 g kg−1 DM) and digestible energy (12.73, 12.50 and 12.25 MJ kg−1 DM) were different (P < 0.05). The crude protein content of the WAS diet was higher (P < 0.05) than that of the PAH diet (164 vs. 154 g kg−1 DM). Average DM intakes (21.8, 22.5 and 21.2 kg d−1) and solids-corrected milk yields (26.9, 27.9 and 26.6 kg d−1) were similar for the three treatments. Also there was no treatment effect (P > 0.05) on milk composition and acetate/propionate ratios of rumen fluid. Thus WAS and PAH diets supported similar production and equalled the low fiber control diet. Key words: Lactation, urea, corn silage, alfalfa, wilted silage, propionic acid treatment.

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