The objective of this study was to compare triticale dried distillers grains plus solubles (TDDGS) as a source of dietary N with other high-protein feeds commonly used in North America: corn dried distillers grains plus solubles (CDDGS), canola meal (CM), and soybean meal (SBM). Rumen degradable protein (% of crude protein, CP) after 16h of incubation in the rumen was higher for CDDGS and TDDGS (69.3% and 64.5%, respectively) than for CM (62.2%) and SBM (53.0%). For the lactation study, experimental diets were formulated to supply 30% of dietary CP from TDDGS, CDDGS, CM, or SBM. These diets contained 22.3% forage neutral detergent fiber and approximately 19.2% CP and were fed to 12 multiparous Holstein cows (130+/-40 d in milk) in a 4 x 12 Latin rectangle design with 21-d periods. Neither dry matter intake nor milk yield was affected by treatment, averaging 25.5 and 35.5kg/d, respectively. Plasma concentrations of Arg, Lys, and Thr were greater for cows fed CM or SBM compared with those fed TDDGS or CDDGS, whereas plasma concentrations of Leu and Phe were lower for cows fed CM or SBM compared with those fed TDDGS or CDDGS. Cows fed CDDGS had lower milk CP yield compared with cows fed CM (1.07 vs. 1.16kg/d). Contrarily, milk CP and milk lactose yields were not different for cows fed TDDGS compared with CM or SBM. These data suggest that TDDGS can replace CM or SBM in the diets of lactating dairy cows without adverse effects on production. Furthermore, although dried distillers grain has been generally accepted as a feed high in ruminal undegradable protein, CDDGS and TDDGS used in the present study had high in situ ruminal degradable crude protein. Further investigation is warranted to determine the extent of variation in ruminal protein degradation among different types of dried distillers grains.