Comparison of three in vitro methods for determining and predicting the organic matter digestibility of complete diets for ruminants

In this study, the organic matter digestibility (OMD) of six complete diets for ruminants has been determined in-vivo in trials with sheep and in-vitro using two-stage Tilley and Terry (T&T) method, gas production (GP) technique and multi-enzyme incubation (EDOM) procedures. The mean OMD values obtained in vivo and using T&T, GP and EDOM techniques were 684, 716, 685 and 710 g OM/kgDM respectively and did not differ significantly (P>0.05). The obtained in vitro results were regressed against determined in-vivo values to derive prediction equations. Using the T&T technique, the prediction equation OMD (in_vivo) = -17.36 + 0.98 x OMD (in_vitro_T&T), (R2 = 0.75; RMSE = 37.59) has been obtained. The equation OMD (in_vivo) = 198.98 + 0.71 x OMD (in_vitro_GP), (R2 = 0.21; RMSE = 66.36) has been derived for Gas production procedure, while the equation OMD (in_vivo) = 102 + 0.82 x OMD (in_vitro_EDOM), (R2 = 0.86; RMSE = 27.30) has been generated for multi-enzyme incubation technique. The results of this study showed that the OMD of complete diets for ruminants can be successfully determined, and in-vivo values predicted, using multi-enzyme incubation procedure, which is important because of the fact that rumen liquor, needed for the in-vitro twostage T&T and GP techniques is not always available to analytical laboratories