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 fibe r digestibility as part of a total mixed diet on intake and production of cows with intakes that were likely limited by rumen fill, using tr eatments that were not confounded by fiber source, concentrate, or rat io of forage to concentrate. Two alfalfa silages with similar NDF conc entrations (40%) but different NDF digestibilities (40 vs. 45% after 2 4 h of in vitro fermentation) were harvested, mixed with concentrate t o achieve diets containing 35% NDF, and offered to 12 multiparous cows (13 DIM) in a two-period balanced crossover design. Samples taken dur ing silage feeding revealed that diets differed in both NDF digestibil ity (3 percentage units) and NDF content (1.8 percentage units), makin g interpretation of results difficult. Nonetheless, milk production (3 6.3 vs. 38.2 kg/d) and DMI (19.4 vs. 20.4 kg/d) were significantly hig her with the higher NDF digestibility diet. Apparent in vivo DM and ND F digestibilities, total rumen VFA after feeding, and molar percentage of propionate were also higher with this diet. Equal NDF intake betwe en diets suggested that higher DMI was due to the lower NDF content in the more digestible NDF diet. Higher NDF digestibility might also inc rease DMI; further experimentation is necessary with larger unconfound ed differences in fiber digestibility at the time of feeding.