USE OF A MULTIEXPONENTIAL MODEL TO ASSESS THE EFFECT OF FERMENTATION IN THE RETICULORUMEN ON PARTICLE FRAGMENTABILITY AS SIMULATED FROM ARTIFICIALLY MACERATING LEAF AND STEM FRACTIONS OF 2 TROPICAL GRASSES

This study reports the use of a mechanical macerating device to charac terise the patterns of, and resistance to, fragmentation of leaf and s tem fractions of spear grass (Heteropogon contortus) and sabi grass (U rochloa mosambicensis). The four substrates, cut to a length of 1.5-2 cm, were exposed to microbial fermentation in the rumen of cattle for periods of between 0 and 96 h. A novel macerating device was used to g rind substrates in a water medium for a series of predetermined number of rotor revolutions of the macerater. The extent of fragmentation wa s then measured by wet sieving. Statistical modelling, using phase-typ e distributions, was used to describe the numbers of revolutions requi red to fragment the substrates into three compartments defined by part icles retained on screens of 1180, 600, and 50 mu m pore size, The stu dy identified multi-exponential patterns of fragmentation of tropical grass fractions, Resistance to fragmentation of large particles, estim ated by the number of rotor revolutions required fur 0.75 of particles to be removed from that pool, was high for both stem fractions, and w as not markedly affected by time of microbial fermentation, Spear gras s leaf had high resistance to fragmentation until exposed to microbial fermentation for 24 h, after which it attained the low resistance to fragmentation typical of sabi grass leaf at all microbial fermentation times.