Nutritive evaluation of herbage from permanent meadows by near-infrared reflectance spectroscopy:: 2.: Prediction of crude protein and dry matter degradability

A total of 62 herbage samples, harvested in natural meadows located in the uplands of Leon (northwestern Spain) and characterised by a diverse botanical composition and different stages of maturity of the plants, were used to evaluate the ability of chemical composition and near-infrared reflectance spectroscopy to predict dry matter (DM) and crude protein (CP) ruminal degradability. Three nonproductive Holstein-Friesian cows fitted with rumen cannulae were used to incubate the herbage samples. Once the DM and CP disappearance rates had been calculated, the exponential model of McDonald was fitted to estimate the kinetic parameters, which were used to calculate the potential and effective ruminal degradability at different passage rates. A Bran+Luebbe InfraAlyzer 500 spectrophotometer was used to obtain the near-infrared (NIR) spectra corresponding to the 62 original herbage samples. Prediction equations for the estimation of the DM and CP degradability parameters were generated using the chemical composition data and the NIR spectra as independent variables. The results showed that the kinetic parameters were predicted with less accuracy than the potential or effective degradability of the chemical fractions. When NIR spectra were used as independent variables, the accuracy of the predictions of the potential or effective degradability of DM and CP was higher. Overall, the degradability of CP was predicted less successfully than the degradability of DM, probably owing to errors in the reference method, such as the microbial contamination of the incubation residues. (c) 2005 Society of Chemical Industry.