PREPARATION OF PROTEASE FROM MIXED RUMEN MICROORGANISMS AND ITS USE FOR THE IN VITRO DETERMINATION OF THE DEGRADABILITY OF TRUE PROTEIN IN FEEDSTUFFS

Abstract

Mixed rumen microorganisms present in bovine rumen fluid were extracted with butanol-acetone to provide a dry powder which retained 75–80% of the proteolytic activity of strained rumen fluid (SRF). Sixty percent of the proteolytic activity of the powder was extracted with water and concentrated on an Amicon XM-300 filter to give a protease preparation which had about 30% of the activity present in the SRF. The protease preparation was used for the determination of the rates of feed protein degradation in vitro by incubating at pH 6.8 in 0.1 M potassium phosphate buffer and measuring the rate of amino acid (and ammonia) production by the ninhydrin method. The relative degradation rates of the true proteins from feedstuffs tested were: soybean meal > fish meal > linseed meal and blood meal > canola meal > corn gluten meal. Substituting Streptomyces griseus protease for the rumen protease gave results which were very different from those obtained with the rumen enzyme. The advantages of using the rumen protease over other in vitro methods and the practical applicability of the procedure are discussed. Key words: Rumen, protease, preparation, in vitro, feed protein degradability