Prediction of the digestibility of the primary growth of grass silages harvested at different stages of maturity from chemical composition and pepsin-cellulase solubility

Relationships between silage chemical components or organic matter (OM) pepsin-cellulase solubility and in vivo organic matter digestibility (OMD) and D-value (digestible OM content in dry matter) were studied. Twenty-five silages were made from primary growth timothy-meadow fescue swards in 6 years (3–6 silages per year) at 6–10 days intervals. The silages were analyzed for chemical composition, in vitro pepsin-cellulase solubility and in vivo digestibility in sheep. Chemical components of silage were highly correlated with OMD and D-value, but the accuracy of the OMD and D-value prediction equations were not satisfactory for ration formulation. Acid detergent fibre was the best single predictor of chemical parameters explaining 0.80 of the variation in OMD (residual mean square error (RMSE) 27.2 g kg−1). Relationships between crude protein (CP) and lignin were improved, when the effects of year or year × component interaction were included in the model. For CP the intercepts and for lignin the slopes, were different between the years. Pepsin-cellulase solubility was superior to chemical parameters in predicting silage OMD and D-value. The monovariate regression equation between OM solubility and OMD was: OMD (g kg−1)=97+0.87×OM solubility (R2=0.974; RMSE=10.8 g kg−1). Prediction of D-value was improved by including ash as a second factor in bivariate regression analysis: D-value (g DOM (kg DM)−1)=160+0.818×OM solubility −1.09×ash (R2=0.974; RMSE=9.7 g kg−1). It was concluded that OM pepsin-cellulase solubility has great potential in predicting silage OMD and D-value both precisely and accurately.