Relationship between chemical composition and in situ rumen degradation characteristics of grass silages in dairy cows

The DVE/OEB2010 system in the Netherlands uses a large database of in situ rumen incubations with grass silage and grass hay samples to derive prediction formulas to estimate the rumen degradation characteristics of a number of feed value parameters. These in situ rumen incubations were not performed for this specific purpose and the data were generated at different research institutes over more than 40 years, using different grass management and fertilization practices and using different protocols. The objectives of this study were to 1) generate a new database on the rumen degradability of dry matter (DM), organic matter (OM), crude protein (CP) and neutral detergent fibre (NDF) of grass silages, 2) compare this new database with the old database used in the DVE/OEB2010 system, and 3) derive regression equations using the new database to investigate the relationships between chemical composition and in situ ruminal degradation characteristics of DM, OM, CP and NDF of the grass silages. Sixty nine grass silages, with a broad range in chemical composition and quality parameters, were selected and incubated using the nylon bag technique in the rumen of three lactating Holstein Friesian cows for 2, 4, 8, 16, 32, 72 and 336 h. There was a large range in the rumen degradable fractions of DM, OM, CP and NDF of the grass silages at each rumen incubation period. The data on the rumen degradation characteristics of DM, OM, CP and NDF in the present study were determined using the same standard incubation protocol, the same cows, and the same chemical analysis procedures for all the grass silage samples. Regression analysis, using the new database, showed relationships between the washable (W) fraction, rumen undegradable (U) fraction, potentially rumen degradable (D) fraction and effective rumen degradation (ED) of DM, OM, CP and NDF, respectively, and the chemical composition of the grass silages.