Canola meal (CM) has been shown to be a more effective CP source than soybean meal (SBM) for lactating dairy cows. Treating CM may increase its RUP fraction and improve the amount of absorbable AA. The objective of this study was to evaluate the effects of feeding treated CM (TCM) on performance of dairy cows. Forty-five Holstein cows were blocked by parity and DIM and used in a study of randomized complete block design. Cows were fed a control diet for a 2-week covariate period and then switched to the experimental diets for a 12-week study. Treatments differed only in CP source and were SBM, CM, and TCM. All diets contained (DM basis) 30% alfalfa silage, 30% corn silage, 4% soy hulls, 2.4% mineral-vitamin premix and 16% CP. SBM diets contained 25% high moisture corn (HMC) and 8.6% SBM; CM diets contained 22% HMC and 11.4% CM. Data were analyzed using the mixed procedure of SAS. Orthogonal contrasts were used to compare effects of different protein sources (SBM vs. CM + TCM) and (CM vs. TCM). There were no statistical differences in DMI and milk yield among diets; however, CM diets had numerically higher milk yields (Table 1). Compared with SBM both CM diets decreased MUN concentration (P = 0.02). There were no significant differences in milk composition and yields among treatments. Results from this study suggest that CM diets may improve N utilization, as indicated by reduced MUN. Although the large numeric differences in milk production were not statistically significant, these differences may be important from a practical standpoint. Table 1. Dry matter intake, milk production, and composition results

Item	Treatment			SEM	Contrast probability
SBM	CM	TCM	SBM vs. CM + TCM	CM vs. TCM
DMI, kg/d	25.9	26.5	27.1	0.90	0.44	0.70
Milk, kg/d	39.4	40.3	41.9	1.34	0.32	0.46
FCM, kg/d	41.2	45.2	43.7	1.96	0.16	0.66
FCM/DMI	1.64	1.67	1.70	0.06	0.53	0.79
Fat, %	4.16	4.18	4.14	0.15	0.99	0.93
Fat, kg/d	1.55	1.60	1.67	0.08	0.33	0.63
Protein, %	3.18	3.12	3.22	0.06	0.95	0.34
Protein, kg/d	1.18	1.21	1.30	0.05	0.26	0.33
Lactose, %	4.83	4.91	4.89	0.05	0.26	0.80
Lactose, kg/d	1.77	1.85	2.00	0.10	0.20	0.41
SNF, %	8.91	8.95	8.95	0.07	0.72	0.99
SNF, kg/d	3.32	3.43	3.68	0.17	0.25	0.41
MUN, mg/dL	14.0	12.9	12.5	0.40	0.02	0.49