ARS | Publication request: Effect of Level of Rumen Degradable Protein on Milk Production, Rumen Metabolism and N Utilization in Lactating Dairy Cows

Submitted to: Journal of Dairy Science
Publication Type: Abstract
Publication Acceptance Date: July 25, 2002
Publication Date: N/A

Technical Abstract: Twenty eight (8 ruminally cannulated) lactating Holstein cows were blocked by DIM, and randomly assigned to seven 4 x 4 Latin squares (2 squares of cannulated cows) to determine the effect of different levels of dietary RDP on milk production, rumen metabolism and urinary and fecal N excretion. Diets were formulated from corn silage, alfalfa silage, high moisture corn, solvent soybean meal, SoyPass$^{\registered}$, urea, vitamins and minerals to provide similar levels of CP coming from ingredients other than urea. Solvent soybean meal, SoyPass and urea in the diets were adjusted to achieve RDP levels of 11.6, 10, 8.3 and 6.6% of diet DM for diets A, B, C and D, respectively. DMI, milk and milk fat production averaged 25.5, 42.8 and 1.3 kg/d across diets and were not different. Milk protein content was higher (P<0.01) for diet B than for diets C and D (3.09 vs. 3.00 and 2.97%) and intermediate for diet A (3.07%). Milk protein yield was higher (P<0.05) for diets A and B than for diet D (1.31 and 1.34 vs. 1.24 kg/d) and intermediate for diet C (1.29 kg/d). Milk urea N was higher (P<0.01) for diets A and B than for diets C and D (13.0 and 13.2 vs. 11.4 and 11.3 mg/dl). Cows fed diet A had the highest (P<0.01) urinary N and urine volume when compared to diets B, C and D (319 vs. 270, 255 and 224 g/d; and 28.0 vs. 19.7, 21.5 and 20.3 l/d, respectively). Cows fed diet D had the lowest (P<0.01) urinary N excretion (224 g/d) when compared to other diets. Decreasing dietary RDP levels from 11.6 to 8.3% reduced urinary N excretion by 64 g/d without affecting milk and protein yield, but diet D with 6.6% RDP decreased N excretion but also depressed milk production.