A Comparison of In Vitro Fermentation and Chemical Solubility Methods in Estimating Forage Nutritive Value

Abstract

The digestibility of cellulose in 12-hr, in vitro rumen fermentations (IVCD), solubility of cellulose in cupriethylenediamine (CED), and solubility of dry matter in 1.0 N H2SO4 (DMS) was determined for 65 forages including 22 grasses, 17 alfalfa, and 26 mixed forage hays. The same forages were fed to sheep in digestion trials to determine apparent digestibilities of dry matter (DMD), cellulose (CD), energy (ED), and protein as well as relative intake (RI) and Nutritive Value Index (NVI). Correlation and regression coefficients were determined for the relationships between the laboratory and in vivo measurements. The correlation coefficients varied considerably depending on which class of forages and which in vivo measurements were being considered. IVCD measurements were more highly correlated with in vivo measurements for grasses, while CED, DMS, or both, were better for alfalfa or mixed forages. The best correlations were obtained when either IVCD or CED values were combined with the DMS data. Further addition of independent variables to the multiple regressions were of little value in increasing the size of the correlation coefficient. Considerably more between day (or run) variation occurred in the IVCD method, presumably due to inoculum variation.