The Accuracy of Pepsin-Cellulase Technique for Estimating the In Vivo Metabolizable Energy Values of Maize Silage and Dry Forages

Objective: The aim of this study was to examine the validity of chemical composition and pepsin-cellulose solubility in predicting in vivo metabolizable energy (ME) values of maize silages and dry forages to develop prediction equations for routine use. Materials and Methods: Forty samples of maize silage and dry forages of known in vivo ME were used to compare an in vitro method with pepsin followed by cellulase technique. Dry forages were alfalfa hay, grass hay and wheat straw (n=30). For this reason, simple or multiple linear regression analysis with pepsin-cellulase solubility (ELOS) or insolubility (EULOS) and the chemical composition was used to establish equations for the prediction of ME. Results: The pearson correlation coefficients (r) were found significantly important between in vitro and in vivo ME for maize silages (r = 77.6, % and p= 0.008) and dry forages (r = 81.8, % and p= 0.000). While the highest determination coefficient (R2) value (72.3, %) using single chemical composition with EULOS were obtained with crude fiber, the combination ash and ether extract gave best R2 value (88.3,%) with EULOS for maize silages. Adding more than four chemical compositions with ELOS did not improve the R2 values (80.4, %) for dry forages. Conclusion: In conclusion, a reasonably acceptable prediction equation of ME values of maize silage could be made by using ash, crude protein, ether extract and crude fiber or nitrogen free extract with EULOS. Adding more than four chemical compositions with ELOS did not improve the R2 of ME values of dry forages. Further work is needed to found the causes of variability in predictive equations and significance of environmental and other factors