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Feed Processing. VIII. Estimating Microbial Protein in Rumen Fluid with Presipitating Agents or in Incubated Mixtures of Uncooked Grain Plus Urea or Starea with Differential Centrifugation¹

Department of Dairy and Poultry Sciences, Kansas State University, Manhattan 66506

ABSTRACT

Four protein precipitating agents (trichloroacetic, perchloric, picric, and tungstic acids) were compared for their ability to estimate the quantity of microbial protein in rumen fluid. Trichloroacetic acid proved the best precipitating agent among the four; however, because of conflicting results of other workers, another method was sought. Differential centrifugation was used to separate bacteria quantitatively from in vitro fermentation mixtures. However, when cooked substrates like Starea were used, a polysaccharide slime draped the bacteria and prevented their separation. To overcome that problem, differential centrifugation was discarded, and a direct high-speed centrifugation and methanol-extraction procedure was used. This method estimated adequately microbial synthesis when cooked and uncooked substrates were compared.

¹ Contribution no. 901, Department of Dairy and Poultry Sciences, Kansas Agricultural Experiment Station, Manhattan.

² Present address: Feed Services, Inc., P. O. Box 482, Caldwell, ID 83605.