Use of Nitrogen from Ammoniated Alfalfa Hay, Urea, Soybean Meal, and Animal Protein Meal by Lactating Cows

Abstract

Midbloom alfalfa hay was baled (16% moisture) and treated with approximately 2% anhydrous NH3 (percentage of DM). Concentrations (percentage of DM) of total N (4.7% vs. 3.4%), NPN (1.3% vs. 0.4%), soluble N (14.8% vs. 8.2%), RUP (6.3% vs. 4.8%), and NDF (52.5% vs. 45.7%) were higher 3 wk after ammoniation than before treatment. Diets (15% CP) that provided 26% of total CP from N added to hay by ammoniation, urea, soybean meal, or a commercial blend of animal protein meals were fed to lactating cows. All diets provided concentrations of CP and RUP as recommended by the NRC, but diets with ammoniated hay, urea, and soybean meal provided only 70% of NRC recommendations for RUP (100% for the animal protein diet). Apparent digestibilities of DM, N, and fiber fractions were not affected by diet. Diet did not affect N balance, but cows fed the urea diet excreted more N in urine and had higher concentrations of ruminal NH3 and plasma urea than did cows fed ammoniated hay. Production (30 kg/d) and composition of milk and DMI were largely unaffected by diet. Diverse sources of dietary N did not greatly influence N utilization by dairy cows.