Comparison of laboratory methods on precision and accuracy of predicting forage organic matter digestibility

Abstract

Three methods of estimating digestibility were tested using different incubation times. A modified one-stage in-vitro method (VOS), an in vitro true digestibility (IVTD) at two incubation times and an in sacco true digestibility (ISTD) method, also at two incubation times were examined for precision and accuracy of prediction. Forages ( n = 21) consisting of straws, hays and silages, grown in Sweden and of known in vivo organic matter digestibility (OMD) running from 0.300 to 0.809 were used. Incubations of single samples replicated on 3 different days were used. Fermentation times were 96 h (standard) for the VOS and 48 h (standard) and 72 h for the IVTD and ISTD methods. Results showed higher mean OMD at 72 h (0.78) than at 48 h (0.75) and higher values for ISTD (0.79) than for IVTD (0.74) and for VOS (0.70). The reliability of the results (precision) was poorest with the in sacco methods. Variations in precision among the in vitro techniques were small. The intercepts decreased and the slopes of the regression equations increased, when incubation time changed from 48 to 72 h. The accuracy of predicting in vivo digestibility was lowest with IVTD and ISTD incubated at 72 h followed by ISTD and IVTD at 48 h and highest with VOS.