The potential digestibility of leaf and stem fractions of grasses

Abstract

SummaryThe potential digestibility of leaf and stem fractions of Rhodes grass (Chloris gayana) and Pangola grass (Digitaria decumbens) were determined by incubating in vitro with rumen fluid for 4, 7, 11 and 14 days with reinoculation after 7 days. The mean drymatter solubility (DMS) of four leaf and four stem samples from the two species, increased from 53·6% after 4 days to 63·8% after 14 days with increases of 14·9 and 5·7% for leaf and stem respectively. Prolonged incubation of sheep faeces from these feeds gave similar patterns of DMS as those for the original feed.To determine the cause of the observed rise in DMS, leaf and stem of Rhodes grass was incubated for 21 days with rumen fluid and Onozuka cellulase. When using cellulose, DMS increased by 7·7% compared with 14·6% when using rumen fluid. The higher DMS with rumen fluid was associated with an increase in the mean disappearance of lignin from 33·6% at 4 days to 52·6% after 21 days. After 14 days there was no further loss of lignin from most samples indicating the existence of a hard resistant lignin core.It was concluded that when determining potential digestibility forages must be incubated with rumen inoculum for at least 21 days and that shorter incubation times may lead to biased conclusions.