Barley (Hordeum vulgare, L.) harvested at boot (5/7/88) and soft dough (6/6/88) stages of maturity was ensiled for nutritive comparisons. Boot stage was wilted and soft dough was direct cut at 15 (SD-Lo) and 25 cm (SD-Hi) above ground. Yields (kg DM/ha) were 3690, 8750 and 6287 for boot, SD-Lo and SD-Hi respectively. Digestibilities (%) of DM, CP and ADF were 74.7, 74.5 and 70.8 for boot; 61.9, 50.4 and 44.7 for SD-Lo; and 62.3, 47.2 and 49.7 for SD-Hi, respectively. Calculated TDN was 71.2, 62.0 and 62.8 for boot, SD-Lo and SD-Hi, respectively. Thirty-six lactating Holstein cows were fed boot silage at 75 and 60% of diet DM, SD-Lo fed at 75 and 60 and SD-Hi fed at 75 and 60, respectively. Milk yields (kg/d) were greatest for high concentrate diets and averaged 25.7, 28.3, 24.8, 26.3, 25.7 and 26.9, respectively. There were no differences among diets for DM intake or 4% FCM. Boot silage had a greater In Situ rumen degradability of DM, CP, ADF and NDF (68.6, 89.3, 44.2 and 45.1% respectively) than SD-Lo (57.8, 76.9, 20.9 and 24.2%) and SD-Hi (62.5, 80.0, 22.8 and 26.4%). Predictability of ruminal degradability of complete diets from weighted averages of single ingredients determined separately was low. In Situ incubation of single ingredients resulted in underestimation of DM and overestimation of CP degradability compared with complete diet incubation. / Master of Science