Rate of Plant Cell Wall Particle Size Reduction in the Rumen

A wether with ruminal and duodenal fistulae was fed orchardgrass pellets in meals 2h apart to obtain “steady state” conditions in the gastrointestinal tract. Six experiments were conducted to determine the size distribution of cell wall particles that escaped the rumen and to determine the rate of reduction of cell wall size. The wether was given intraruminal doses of carbon-14 labeled plant cell walls of varying particle size and lignification in five 13-day experiments. Cell wall digestibilities of the basal diet were repeatable (76.9±.6) and ranged from 75.8 to 77.5% for six experiments, including a control experiment without a ruminal dose of carbon-14 labeled cell walls. Cell wall particles with a mean size of 5.3 μ (.2mm) escaped from the rumen with essentially no reduction of size. Mean sizes of samples collected from duodenum and feces support the 5.3 mean natural logrithm. In addition, a natural logrithm size in the order of 5.3 is supported by a proposed asymptotic model describing cell wall reduction from single doses of carbon-14 labeled plant cell walls. The rate of cell wall reduction appears to be inversely proportional to the mean size of particles in the rumen at time zero. This methodology and the asymptotic model should have application to study further the importance of reduction of cell wall particle size in limiting voluntary intake of forages.