Investigation of dry matter degradation and acidotic effect of some feedstuffs by means of in sacco and in vitro incubations

The dry matter degradation in the rumen and pH decrease of nine primary feedstuffs, three compound feeds and three combinations of each two primary feedstuffs, were evaluated by means of in sacco and in vitro incubations. The ingredients included barley, wheat, manioc, maize, sorghum, sugar beet pulp, soya-bean meal, soya-bean hulls and maize gluten feed. The compound feeds differed in content and composition of the starch and sugars fraction, as well as in fibre content. The three combinations each consisted of a rapidly and slowly degradable feedstuff. The feedstuffs were incubated for different times to examine optimal incubation conditions for both estimating methods. For the in sacco technique, best predictions were obtained after 3 h of incubation. In this way, ingredients were ranked in order of decreasing dry matter degradation: manioc, wheat, barley, maize gluten feed, beet pulp, soya-bean meal, maize, sorghum, soya-bean hulls. With the in vitro method, better results were observed when rumen fluid was taken after rather than before feeding. After 5 h of incubation, ingredients were ranked in order of declining pH decrease: manioc, wheat, beet pulp, maize gluten feed, barley, maize, soyabean meal, sorghum, soya-bean hulls. Except for beet pulp, in vitro ranking agreed fairly well with in sacco results. The validity of these techniques was examined by limited results of in vivo experiments, where the effect of the nature of the compound feed on rumen fermentation was investigated. In vivo, a clear difference in risk for rumen disturbances could be observed between the three compound feeds. In sacco and in vitro, however, the compound feed with the high content of slowly degradable starch, could hardly be distinguished from the crude fibre rich compound feed. As only a limited amount of in vivo material was available, the estimating value of these methods require confirmation.