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Degradation of Crude Protein in Forages Determined by In Vitro and In Situ Procedures¹

Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061

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ABSTRACT

Objectives were to determine in selected forages fiber and protein fractions, in vitro and in situ CP degradability, and to compare in vitro methods of estimating rumen CP degradability with the in situ bag technique. Forages analyzed (five samples per treatment except alfalfa hays, which had four) included alfalfa as baled hay, alfalfa ensiled in conventional upright silos, alfalfa ensiled in oxygen-limiting silos, ammonia-treated corn silage, untreated corn silage, and orchardgrass hay. Untreated corn silages had the greatest protease insoluble CP at 48 h, indicating protein in corn silage is not degraded well by protease enzyme. In situ CP degradability was greater than 80% for all ensiled forages. Ensiled forages had the greatest estimated A fraction (rapidly degraded in the rumen), alfalfa hays had the greatest B fraction (intermediate rate of degradation), and orchardgrass hays had the greatest C fraction (not degraded in rumen).

High correlations between in situ degradability and some in vitro measurements suggest laboratory techniques of estimating CP degradability of forages are possible. For silages, buffer-soluble CP had the greatest correlation (.58) with in situ degradability; for hays, NDIN had the greatest correlation (–.83).

¹ Data were taken from a dissertation submitted to Virginia Polytechnic Institute and State University by F. J. Janicki to fulfill partial requirements for the Ph.D. degree.

² Current address: Dairy Nutrition Services, Inc., Chandler, AZ 85224.

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