Predicting Diet Protein Degradability from Individual Ingredient Estimations In Diets Containing Barley Silages

Whole plant barley was ensiled in 3-by 12-m silos at boot and soft dough growth stages. Boot barley was wilted before ensiling, and soft dough was direct-cut at 15 cm (low cut) and 25 cm (high cut) above ground. Diets containing each silage at 75% (high forage) and 60% (low forage) of diet DM were incubated for 0, 2, 12, 24, and 72 h in situ in two ruminally fistulated, lactating Holstein cows. Individual silages, 44% CP soybean meal, and ground shelled corn were incubated similarly. Feedstuff CP degradabilities were 89.3, 79.6, 83.4, cut, soft dough-high cut, soybean meal, and corn. Degradabilities of CP for complete diets were 82.0, 81.7; 77.8, 71.5; and 77.6, 76.9% for boot, high and low forages; soft dough-low cut, high and high and low forages, respectively. Using individual feed determinations, estimates of diet degradability resulted in no consistent trend [degradability determined (on complete diet) minus predicted (from individual feedstuffs): -.7, means were within 5% of determined ones.