Effect of alfalfa grass silage dry matter content on ruminal digestion and milk production in lactating dairy cows

In trial one, seven lactating Holstein cows fitted with rumen cannulae were used in a replicated 3 × 3 Latin square design to investigate the effect of feeding alfalfa/grass ensiled at three dry matter (DM) levels (27.5, 46.1 and 56.4%) on the rate and extent of protein degradation. Cows were fed a total mixed ration of 70% alfalfa/grass silage, at one of three DM levels, and 30% concentrate (high moisture corn and mineral) (DM basis). Silage samples were incubated in sacco in the rumen for up to 48 h to model disappearance of DM, neutral detergent fibre (NDF) and nitrogen (N). Passage rates of silage, using Cr-mordanted NDF, were determined for small and total particulate fractions. Rates of DM, NDF and N disappearance, as well as rates of passage were unaffected by silage DM content. The 27% DM silage contained a larger soluble N fraction, but a smaller fraction of potentially digestible N than either the 46 or 56% DM silages. Estimates of effective protein degradability corrected for microbial contamin...