Potential Reduction of Forage and Rumen Digesta Particle Size by Microbial Action

Abstract

Abstract Our objective was to examine direct effects of microbial action on particle size of feed and rumen digesta samples. The first experiment examined reduction of particle size during 48-h in vitro fermentation of rumen digesta from steers fed alfalfa hay or hay-concentrate diets. Distributions of particle size of material recovered on sieves were not altered significantly. A second in vitro experiment studied fermentation of a size-defined fraction of coarsely ground alfalfa hay. Over 50% of substrate dry matter and 37% of insoluble dry matter were digested after 48h. Logarithm base 10 of mean particle size was not changed; however, log 10 standard deviation increased linearly with incubation time. This was interpreted to indicate enough size reduction occurred to skew the distribution of particles without changing the mean. In a third experiment the same hay fraction was incubated for 96h in situ. Over 60% of substrate dry matter and 51% of insoluble dry matter were digested in 48h. Logarithm base 10 of mean particle size decreased with time of incubation; however, log 10 standard deviation was not affected. The 19% reduction of mean particle size in situ made only a minor direct contribution to total reduction of size necessary before passage from the rumen would be likely.