The gas-test technique as a tool for predicting the energetic value of forage plants

Abstract

Seventy-nine forages of known in vivo organic matter digestibility (OMD) out of which 45 of known voluntary dry matter intake (DMI) all measured with sheep, were submitted to the in vitro gas production (GP) technique. The aim was to study the prediction accuracy ( R 2 , RSD) of the nutri- tive value of the main components of forages that is, OMD, DMI and voluntary digestible organic mat- ter intake (DOMI). This accuracy was compared with that obtained with the pepsin cellulase method (Cellulase). It appeared necessary to consider the forages by category (grasses or legumes and green forages or hays) in order to obtain a better accuracy in OMD prediction. The (a + b) value of the GP model = a + b (1-e -ct ) used to fit the data did not appropriately predict OMD, which was much better predicted from the c value (related to the rate of fermentation) or by Cellulase. For grass hays, the OMD was already well predicted by GP 24 h 〈 CP (gas produced after 24 hours 〈 crude protein content). The accuracy of digestibility prediction was improved by adding CP as a complementary variable except with lucerne hays. The relationships between DMI and gas production (at a given time or at the end of fermentation) were fair and not really improved by adding CP content. However, the accuracy of DOMI prediction was slightly better with c 〈 CP than with Cellulase for green grasses and grass hays, although Cellulase was better for DOMI prediction of whole lucerne. Although the gas production technique was less efficient than Cellulase to predict OMD it is an interesting tech- nique for predicting voluntary DOMI, that is the global nutritive value of forages. prediction / organic matter digestibility / ingestibility / in vitro gas production / Cellulase / forages / ruminant