Screening Fresh Forages for Protein Degradation and Nutritive Value

A method has been developed to prepare fresh forages for in sacco and in vitro incubation by freezing and mincing to achieve a particle size distribution of dry matter (DM) similar to in vivo conditions. The method is described and data presented to indicate losses of nitrogen (N) during in sacco digestion and net yield of ammonia from proteolysis in vitro for 22 fresh and conserved forages. Grasses, legumes and herbs were evaluated, with fractional degradation rates of forages ranging from 0.07h-1 with tall fescue (Festuca arundinacea) to 0.24 h-1 with chicory (Cichorium intybus). Degradation of protein to ammonia in vitro over 24 h was highest with white clover (Trifolium repens) and about 20% of the nitrogen (N) released during degradation was incorporated into microbial N. These data will assist formulation of forage based total mixed rations for high producing ruminants.