Enhanced intake and production of cows offered ensiled alfalfa with higher neutral detergent fiber digestibility

The objective of this study was to determine the effect of forage fiber digestibility as part of a total mixed diet on intake and production of cows with intakes that were likely limited by rumen fill, using treatments that were not confounded by fiber source, concentrate, or ratio of forage to concentrate. Two alfalfa silages with similar NDF concentrations (40%) but different NDF digestibilities (40 vs. 45% after 24 h of in vitro fermentation) were harvested, mixed with concentrate to achieve diets containing 35% NDF, and offered to 12 multiparous cows (13 DIM) in a two-period balanced crossover design. Samples taken during silage feeding revealed that diets differed in both NDF digestibility (3 percentage units) and NDF content (1.8 percentage units), making interpretation of results difficult. Nonetheless, milk production (36.3 vs. 38.2 kg/d) and DMI (19.4 vs. 20.4 kg/d) were significantly higher with the higher NDF digestibility diet. Apparent in vivo DM and NDF digestibilities, total rumen VFA after feeding, and molar percentage of propionate were also higher with this diet. Equal NDF intake between diets suggested that higher DMI was due to the lower NDF content in the more digestible NDF diet. Higher NDF digestibility might also increase DMI; further experimentation is necessary with larger unconfounded differences in fiber digestibility at the time of feeding.