In vitro digestion of mixtures of grain and hay

Abstract

The digestibilities of the dry matter (DDM) of 16 herbages and 22 mixtures of grain and hay of known in vivo digestibility were determined by a two-stage in vitro technique, with inocula obtained from sheep fed either hay or a diet of 70 per cent barley and 30 per cent hay; both diets contained 12 per cent crude protein. The in vitro digestions were conducted with or without the addition of ammonium sulphate. The correlations between in vivo and in vitro digestibilities were higher for the herbages and the mixtures with inoculum from sheep fed hay, than with that from sheep fed barley and hay. Adding ammonium sulphate to either inoculum lowered the in vivo-in vitro correlation for the mixtures containing grain but improved the correlation for the herbage samples. The variability between replicate in vitro determinations was not reduced by adding ammonium sulphate to the inoculum from sheep fed hay but was increased for the inoculum from sheep fed a mixture of barley and hay.