Abstract
Three sheep fitted with ruminal and duodenal cannula fed hays of early cut (EOG), late cut orchardgrass (LOG) and alfalfa (ALF) were used to identify the size reduction, passage and fiber fermentation of ruminal particles and their relation to fiber digestibility in the rumen. The sample of ingested bolus and ruminal and duodenal digesta were obtained and were fractionated by size using wet sieving (large particles (LP): ⟩5.6mm; medium particles (MP):⟨5.6, ⟩1.18mm; small particles (SP): ⟨1.18, ⟩0.3mm; fine particles (FP): ⟨0.3, ⟩0.047mm). The ruminal digestibility of cellulose was highest for EOG and was higher for LOG than ALF. The cellulose concentration in neutral detergent fiber (NDF) decreased, and the acid detergent lignin (ADL) concentration of ruminal particles increased with size reduction. The rate of size reduction of LP did not significantly differ among hays. The passage rate of particles from the rumen increased with reducing particle size. The rate of passage of SP was smaller for EOG than ALF or LOG, and that of FP was highest for ALF. The slowly digestible fraction tended to become smaller with reducing particle size. The rate of disappearance was higher for MP for EOG and LOG, however, was extremely higher for LP and FP for ALF. It was concluded that the ruminal fiber digestibility was associated with the extent of fiber fermentation occurring with particle size reduction and the difference in passage rate by particle size.
