ESTIMATION OF ORGANIC-MATTER DIGESTIBILITY OF WHOLE MAIZE PLANTS BY LABORATORY METHODS

Relationships between organic matter digestibility (OMD, %) and a range of laboratory measurements have been developed on 43 samples of whole maize plants in trial 1, in 1967 and 1968 and on 118 samples in trial 2, in 1987 and 1988 from three locations in France. Laboratory measurements included two chemical techniques (Weende crude fibre and van Soest methods). one biological technique (in vitro digestibility) and one enzymatic technique (pepsin-cellulase method). Age after flowering and dry matter content were the two parameters best correlated with OMD. The residual standard deviation (RSD) of the prediction was 1.54, taking into account a significant interaction of location on the slope for age and a location of year effect on the interception of the Y axis. As age is not always known in laboratory analysis, it was not included in the predicting equation. All the laboratory techniques allowed the same prediction (RSD about 2 points for 118 samples) but the relationships were significantly affected by year and location. In contrast, OMD is closely correlated with indigestible cell wall content (RSD = 0.53 for 55 samples studied at Clermont-Ferrand). It is concluded that OMD could be better predicted by methods based on in vitro digestibility or pepsin-cellulase digestibility for traditional forages than for whole plant maize.