I. NUTRIENT REMOVAL RATES FROM RUMINORETICULA OF CATTLE GRAZING KANSAS FLINT HILLS RANGE. II. EFFECTS OF SEASON, TIME AND RUMEN SITE ON PARTICLE SIZE CHANGES IN RUMENS OF CATTLE GRAZING FLINT HILLS RANGE

A Hereford steer and heifer were used to compare rumen removal rates of nutrients in forage from Kansas Flint Hills range over a 2-year period. After an overnight fast the rumens were emptied and the contents sampled, weighed and returned to the rumen. Animals were then fed a known amount of range forage and fasted for 12 hours at which time the rumen evacuation procedure was repeated. Removal rate calculations were based on change in rumen contents during the 12-hour fast.;The same cattle were used to study rumen particle size changes during early, growing and dormant seasons. During the first year samples were taken after an overnight fast from 3 rumen sites and the feces early on the sample morning (AM sample). The cattle were fed and sampled again 12 hours later (PM sample). During year 2 the cattle were sampled immediately as they came from the native pasture (PRE sample) in addition to the other 2 sample times. Samples were wet-sieved through a series of 5 screens to separate particle sizes. Material from each screen was weighed and expressed as a percentage of the total of all screens.;In the rumen relative amounts of coarse particles generally decreased while smaller particle amounts increased with advancing season. Seasonal advance lowered percentages of coarse particles at all rumen sites while percentages of smaller particles increased. As rumen residence time increased coarse particle percentages at all sites decreased while particle percentages of the 3 smaller sizes increased at all sites with longer rumen residence time. In the feces coarse particles decreased in percentage while smaller particles increased as seasons advanced.;All nutrients studied passed the rumen more rapidly during spring and summer months than fall and winter months. Comparison of removal rates showed nutrients of lower digestibility to be removed from the rumen more rapidly than more highly digestible nutrients. After 12 hours of digestion percentages of crude protein and cell solubles in rumen digesta were greater than, and percentages of cell walls, cellulose and hemicellulose were less than the percentages of these constituents in the range forage fed.