Prediction of silage digestibility and intake by chemical analyses or in vitro fermentation techniques.

Chemical analyses and in vitro fermentations were on three corn silages, four legume-grass silages, and four corn-hay crop silage mixtures which had been fed to sheep for 21 days. In vivo data were collected for voluntary silage intake and apparent digestibility of energy. Forage nutritive value was expressed as digestible energy intake. Multiple regression equations were developed to determine the more reliable methods to evaluate voluntary intake, digestibility, and nutritive value of silage. Equations for quadratic response surfaces accounted for 71 to 79% of variation in in vivo data compared to 54 to 70% of variability accountable by simple linear regression equations. Dry matter, crude protein, cell wall, acid-detergent fiber, and acid-detergent lignin contents of silage accounted for greater variability in silage intake, digestibility, and nutritive value than did any in vitro method either alone or in combination with chemical analysis. The results support Crampton's concept of nutritive value index, which is now expressed in the relative feed value system proposed by the American Forage and Grassland Council for differences between forages.