Lyophilization of rumen fluid for use in culture media

The supernatant from centrifugation at 1,000 x g of strained rumen fluid was lyophilized, and the residue and sublimate fractions were used to replace fresh rumen fluid in a complete roll tube medium for enumeration of total rumen bacteria. Most of the growth-supporting nutrients in fresh rumen fluid were found in the residue fraction. With one exception, no significant differences were found in total bacterial numbers either by roll tube or most-probable-number procedures when lyophilized rumen fluid residue was substituted for fresh rumen fluid. Lyophilized rumen fluid residue was stable for at least 5 months at room temperature. Rumen fluid supernatant from centrifugation at 1,000 x g had a mean density of 1.005 +/- 0.03 g/ml and contained 1.56% +/- 0.30% dry matter. On the basis of these values, 15.68 mg of lyophilized rumen fluid residue is equivalent to 1 ml of rumen fluid supernatant from centrifugation at 1,000 x g.