INFLUENCE OF STAGE OF MATURITY OF GRASS SILAGES ON DIGESTION PROCESSES IN DAIRY-COWS .2. RUMEN CONTENTS, PASSAGE RATES, DISTRIBUTION OF RUMEN AND FECAL PARTICLES AND MASTICATION ACTIVITY

In four change-over experiments, wilted grass silages, differing in cell wall content (neutral detergent fiber (NDF) content ranging from 44.6 to 67.3% of dry matter (DM)), were fed ad lib. to dairy cows in early and late lactation. The influence of cell wall content of the grass silages on rumen contents and on fractional passage rates of particulate (k(p), %/h) and liquid (k(l), %/h) phases, was determined using Cr-NDF and Tritium (H-3) labeled hay as particulate markers and Co-EDTA as a soluble marker. The k(p) increased with an increase in NDF content of the diet, and with an increase in intake level, whereas the k(l) was not affected by diet composition. Rumen content (total as well as DM, kg) increased with an increasing proportion of concentrates in the diet and thus an increasing DM intake, but did not show any significant relation with silage cell wall content. Total chewing time (CT), rumination time (RT) and eating time (ET) were recorded for six 24 h periods per cow. When the animals ruminated for more than 9 h a day, an increase in cell wall content of the diet did not further increase RT, but resulted in a decreased intake. CT, RT and ET per kg DM tended to increase with an increase in cell wall content, whereas CT, RT and ET per kg ingested NDF tended to decrease. The pool of rumen dry matter (DM) able to flow to the omasum (passing a 1.25 mm sieve), was not influenced by cell wall content of the silages. The pool of rumen DM passing a 0.071 mm sieve, however, decreased with increasing cell wall content. The mean faecal particle size (MFP) significantly increased with cell wall content, and was negatively correlated (r = -0.90, P < 0.001 ) with rumen pool of particles passing a 0.071 mm sieve.