Rumen degradation characteristics of nutrients in maize silages and evaluation of laboratory measurements and NIRS as predictors

From 26 whole crop maize silages the rumen degradation kinetics (the soluble, potentially degradable and undegradable fraction and the degradation rate) of organic matter, crude protein, starch and NDF as well as the digestibility of rumen escape protein in the intestines (%EPdi) were measured with four fistulated cows. The maize silages originated from crops harvested from 1991 to 1998 in the dough dent stage of maturity and involved nine varieties. The fermentable organic matter (FOM), the fractions of protein (%EP) and starch (%ESTA) escaping the rumen, the true protein digestible in the intestines (DVE) and the degraded protein balance in the rumen (OEB) were calculated according to the Dutch protein evaluation system. The mean values and standard deviations were 505 +/- 65 g/kg DM FOM based on in situ data, 556 +/- 38 g/kg DM FOM based on digestible OM, 34.9 +/- 6.6% EP, 72.8 +/- 6.0% EPdi, 26.0 +/- 11.3% ESTA, 55 +/- 4 g/kg DM DVE and -39 +/- 7 g/kg DM OEB. In order to predict these values, regression equations with chemical parameters and the washable fraction (W) as well as NIRS-calibrations were examined. For FOM, %EP, %EPdi and %ESTA, W solely could explain most of the variation. Prediction of DVE and OEB was possible with regressions based on chemical parameters. The predictive ability of NIRS appeared fairly good for %EP, intermediate for FOM and %ESTA and insufficient for %EPdi, DVE and OEB. (C) 2002 Elsevier Science B.V. All rights reserved.