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

¹ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315

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, 77.1, and 71.6% for boot, soft dough-low 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 low forages; and soft dough-high cut, 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, 1.5, 1.7, –3.4, –1.4, and –.2], and all means were within 5% of determined ones.

Key Words: barley silage • in situ degradability

Submitted on March 4, 1991
Accepted on May 31, 1991