Breakdown of large particles in forage by simulated digestion and detrition.

To determine the importance of digestion and detrition (rubbing) in the rumen on the breakdown of large particles (LP) in the leaf and stem fractions of temperate and tropical forages, a study was made using a digestion-detrition simulator. Large-particle breakdown was measured in forage samples subjected to 48-h digestion or 48-h digestion plus detrition. Digestion caused a breakdown of 14% +/- 1.9% (means +/- SE) of the LP, and a further 8 +/- 1.9% were broken down by detrition. There was no difference in breakdown between temperate and tropical forages. The mean breakdown in vitro of LP of temperate forage was similar to that reported in vivo (21 vs 17%), but the breakdown of leaf fraction in vitro was twice that observed in vivo, possibly due to the greater breakdown in vivo of the LP during primary mastication. Both digestion and detrition cause a reduction in size of forage particles in vitro; this result supports conclusions drawn from in vivo studies.