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A Colorimetric Method for the Determination of Proteolytic Degradation of Feed Proteins by Rumen Microorganisms¹

Animal Research Institute, Agriculture Canada, Ottawa, Ontario, Canada, KIA OC6

Abstract

A new colorimetric method for the determination of the degradation of soybean meal by rumen microorganisms in vitro is described. Proteins in soybean meal were diazotized with 7-amino-1,3,naphthalene disulfonic acid. The diazotized meal was incubated at 37 C with rumen microbial suspension (approximately equivalent to 2.0 ml of rumen fluid) in 2.0 ml of. 1M potassium phosphate buffer, pH 7.6. The undigested diazo-protein was precipitated by the addition of perchloric acid and the precipitated protein was solubilized by incubating with crystalline bacterial protease. A portion of the solubilized protein was treated with .15N NaOH and the color intensity was measured at 440 nanometers. Application of the diazo method for the determination of the degradation of soybean meal when present as part of ruminant feed mixture, for evaluating the effectiveness of the protective treatment of soybean meal with formaldehyde and for the determination of solubility of soybean meal in boiled rumen fluid are described.

¹ Contribution No. 756 from the Animal Research Institute.

² The Authors Acknowledge the Technical Assistance of Mr. L. R. Beaton.