IN-SITU DRY-MATTER, PROTEIN, AND FIBER DEGRADATION OF PERENNIAL FORAGES

Eight forages (alfalfa, birdsfoot trefoil, red clover, bromegrass, orc hardgrass, perennial ryegrass, quackgrass, and timothy) at three matur ities were evaluated for ruminal DM, CP, and NDF degradation kinetics. Duplicate dacron bags were incubated for 0, 3, 6, 10, 13, 25, 48, and 72 h in two late lactation Holstein cows fitted with ruminal cannulas over eight experimental periods. Species and maturity effects were ob served for soluble, slow, and undegraded fractions; degradation rate; and ruminally degradable DM, CP, and NDF. Significant species by matur ity interactions also were evident for fractions and ruminal degradabi lities of DM, CP, and NDF. Legumes exhibited more extensive ruminal DM degradation than did grasses. No clear trends were evident in rate of ruminal CP degradation between legumes and grasses. Mature grasses we re lowest in ruminally degradable CP. Legumes exhibited a higher undeg raded fraction and faster degradation rate of slowly degraded NDF frac tions, resulting in similar ruminally degraded NDF for legumes and gra sses. Extensive differences in ruminal degradation kinetics existed be tween perennial legume and grass species and maturities. Species by ma turity interactions were diverse, making categorization of degradation characteristics of legumes and grasses difficult.