Determination of chemical composition, in vitro dry matter digestibility and in vitro gas production of forage by near-infrared reflectance spectroscopy

Abstract

One hundred dried samples of forage, harvested three or four times during 1997 and 1999 in different morphological stages were analysed for chemical composition, in vitro dry matter digestibility (IVDMD; Tilley and Terry, 1963) and in vitro gas production (Menke and Steingass, 1988) by laboratory methods and by near infrared reflectance spectroscopy (NIRS). NIRS predicted the main chemical components, such as crude protein, crude fibre, neutral detergent fibre, acid detergent fibre, with a very high degree of accuracy (i.e. the determination coefficient (R²) varied from 93.5 % for ADF to 98,2 % for NDF), while the coefficients of determination of crude ash, ether extract and acid detergent lignin were 79.6, 85.1 and 82.3 %, respectively, with standard errors of cross validation (SECV) exceeding 9.0 %. The IVDMD was also determined with a high degree of accuracy (R² = 94.3 %; SECV = 4.3 %), such as parameters of gas production "B" (total gas production) and "A" (constant factor describing the decay in specific gas production rate), estimated with the Gompertz model, which have R² and SECV values of 93.0 and 3.8 % and 94.5 and 8.0 %, respectively. The parameter "C" (the specific fermentation rate) was predicted with a somewhat lower degree of accuracy (R² = 78.3 and SECV = 9.6 %).