Microdigestion Techniques and Chemical Solubility Methods as Estimators of the Digestibility of Tropical Grasses

Abstract

The nutritive values of pangola grass (Diptaria decumbens) and kikuyu grass (Pennisetum clandestinum), determined with sheep in conventional digestion trials, were compared with data derived from three indirect methods of estimating digestibility. In vivo measurements were digestible dry matter (DDM), total digestible nutrients (TDN), digestible energy (DE), and cellulose digestibility (CD). Microdigestion techniques consisted of in vitro dry matter disappearance (IVDMD) by two stage fermentation, and nylon bag dry matter disappearance (NBDMD). Solubility was measured in terms of dry matter solubility (DMS) in IN H2S04 and cellulose solubility (CED) in cupriethylenediamine. Pangola grass was more digestible than kikuyu grass by all measurements made. Highly significant differences (P<.01) in nutritive values were detected by both in vivo and indirect methods. Significant differences (P<.01) were noted between microdigestion techniques and DDM. NBDMD was greater than IVDMD and DDM by 8.4 and 12.9 percentage units, respectively, while IVDMD was 4.5 percentage units greater than DDM. Correlations between animal data and both microdigestion techniques were highly significant (P<.01). Of the solubility tests, only CED showed consistently high correlation coefficients. In general, correlations between DMS and animal digestibility were insignificant and lower than CED. There was an unexplained negative relationship, insignificant except for CD (P<.05), between DMS and animal data in pangola grass. In kikuyu grass, correlations between DMS and animal data were insignificant, with the exception of DE (P<.05).