SOURCES OF VARIATION IN THE IN VITRO DIGESTIBILITY OF TROPICAL GRASSES

The in vitro DM digestibility of four tropical pasture species, Cenchrus ciliaris, Chloris gayana, Digitaria spp., Setaria spp. and one temperate grass, Lolium perenne, were studied, using the method described by Tilley and Terry (13). In vitro digestibility was affected by fineness of grinding, sample size, pH of original rumen fluid and size of rumen fluid inoculum. Different relations were found between the in vivo and in vitro results for the five species, with a maximum predicted difference of 3–5 digestibility units. It was considered that the in vivo digestibility of tropical grasses could be accurately predicted by this method, provided that the procedure was standardized and samples of known in vivo digestibility similar to those being tested are included in each run.