INFLUENCE OF STAGE OF MATURITY OF GRASS SILAGES ON PROTEIN DIGESTION AND MICROBIAL PROTEIN-SYNTHESIS IN THE RUMEN

In four change-over experiments, wilted grass silages, differing in gr owth stage at harvesting and as a consequence in cell wall content, we re fed ad libitum to dairy cows in early and late lactation. Ruminal d egradation rate of the crude protein fraction of the silages was inves tigated using nylon bag incubations. No significant relation between t he degradation rate (%h-1) and the cell wall content of the silages wa s found. The soluble and undegradable fractions of the crude protein b oth increased with an increase in silage cell wall content. The solubl e fraction was more closely related to dry matter content and date of harvesting than to cell wall content of the silages. The fraction of d ietary protein escaping rumen fermentation increased with cell wall co ntent. In duodenal protein, the fraction originating from the diet, es timated using amino acid profiles of dietary, microbial and duodenal p rotein, decreased with cell wall content.