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The objectives of this study were to evaluate the effects of feeding high-protein distillers dried grains (HPDDG) on rumen degradability, dry matter intake, milk production, and milk composition. Sixteen lactating Holstein cows (12 multiparous and 4 primiparous) averaging 80 ± 14 d in milk were randomly assigned to 1 of 2 dietary treatments in a 2 × 2 crossover design. A portion of forage and all soy-based protein in the control diet were replaced by HPDDG (20% dry matter). Milk production and dry matter intake were recorded daily and averaged for d 19 to 21 of each 21-d period. Milk samples were collected on d 20 to 21 of each period. Milk yield increased with the inclusion of HPDDG (33.4 vs. 31.6 ± 2.13 kg/d), and 3.5% FCM was higher for the ration containing HPDDG (36.3 vs. 33.1 ± 2.24 kg/d). Percentage protein was not affected by treatment (average 3.04 ± 0.08%), but protein yield increased with inclusion of HPDDG (0.95 to 1.00 ± 0.05 kg/d). Milk fat concentration was not different between treatments (average 3.95 ± 0.20%), but fat yield increased for the ration containing HPDDG (1.35 vs. 1.21 ± 0.09 kg/d). Dry matter intake was not affected and averaged 21.9 ± 0.80 kg across treatments. Because of greater milk production, feed conversion was improved by the inclusion of HPDDG (1.47 to 1.73 ± 0.09). Milk urea N was greater for the HPDDG ration than the control (14.5 vs. 12.8 ± 0.67 mg/dL). This research suggests that HPDDG may effectively replace soy-based protein in lactating dairy cow diets.