Ruminant Nutrition: Nitrogen Sources and Utilization

The objective of this study was to evaluate the effects of replacing protein sources that are commonly used in North America with triticale dried distillers grains with solubles (TDDGS) as a source of dietary N on the productivity of lactating dairy cows. Experimental diets contained 17.1% TDDGS, 17.5% Corn DDGS (CDDGS), 13.1% canola meal (CM), or 10.2% soybean meal (SBM) on a DM basis so that each feedstuff supplied 30% of total dietary crude protein (CP). All diets, which were formulated to contain 17.2% CP and 21.2% forage neutral detergent fiber (NDF), were fed to twelve multiparous Holstein cows (130 ± 40 days in milk) in a replicated 4 × 4 Latin square design with 21-d periods. Plasma concentrations of arginine, lysine, and threonine were greater for cows fed CM or SBM compared to those fed TDDGS or CDDGS (P < 0.01) while plasma concentrations of leucine and phenylalanine were lower for cows fed CM or SBM compared to those fed TDDGS or CDDGS (P < 0.05). Dry matter intake and milk yield were not affected by treatment (25.5 and 35.5 kg/d, respectively). Cows fed CDDGS had a lower plasma glucose concentration (P = 0.04; 49.3 vs. 53.5 and 52.6 mg/dL, respectively), and decreased yields of milk CP (P < 0.01; 1.01 vs. 1.17 and 1.14 kg/d, respectively), and milk lactose (P = 0.03; 1.43 vs. 1.66 and 1.59 kg/d, respectively) compared to cows fed CM or SBM. Cows fed TDDGS had similar plasma glucose concentration (53.5 mg/dL), and milk CP (1.10 kg/d), and milk lactose (1.57 kg/d) yields as cows fed CM or SBM. Furthermore, cows fed TDDGS or SBM had a greater body weight gain compared to cows fed CDDGS (P = 0.05; 514 and 390 vs. -290 g/d, respectively). These data suggest that TDDGS can replace CM or SBM in the diets of lactating dairy cows without adverse effects on production, and may be better N source than CDDGS.