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

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).