The objectives of this study were to evaluate production performance, milk fatty acid composition, and nutrient digestibility in high-producing dairy cows consuming diets containing corn or hull-less barley. Eight primiparous (580 ± 41 kg of BW and 49 ± 18 DIM) and 16 multiparous (650 ± 60 kg of BW and 59 ± 25 DIM) Holstein cows were assigned to 1 of 4 diets in a replicated 4x4 Latin square design with 21-d periods. Cows were fed once daily (1200 h) by means of a Calan gate system. Treatments consisted of diets containing 100% corn (0B), 67% corn and 33% hull-less barley (33B), 33% corn and 67% hull-less barley (67B), and 100% hull-less barley (100B) as the grain source. Total-tract nutrient digestibility was estimated using lanthanum chloride (LaCl₃) as an external marker. The statistical model included the effects of square (fixed; df = 5), treatment (fixed; df = 3), square by treatment interaction (fixed; df = 15), period (random; df = 3), and cow within square (random; df = 18) and the random residual error. Dry matter intake differed quadratically among treatments (P < 0.01), being lowest for 67B (24.3 kg/d) and highest for 0B (26.9 kg/d). Feeding hull-less barley did not affect milk yield (41.4 kg/d, P < 0.98). Milk fat concentration differed cubically among treatments (P < 0.03), being lowest for 0B (3.43%) and highest for 67B (3.91%). Neither the concentrations in milk of protein (3.02%, P < 0.33) and lactose (4.82%, P < 0.58) nor the yields of protein (1.24 kg/d, P < 0.23) and lactose (1.98 kg/d, P < 0.30) differed among treatments. The proportion of de novo synthesized fatty acids in milk did not differ among treatments (P < 0.43). The apparent total-tract digestibility of dry matter (61.5%, P < 0.82), crude protein (61.1%, P < 0.28), and neutral detergent fiber (37.3%, P < 0.38) did not differ among treatments. The apparent total-tract digestibility of starch increased quadratically (P < 0.02), being lowest (97.3%) for 0B and highest (97.9%) for 67B, although these differences are biologically minor. In conclusion, hull-less barley grain is as good as corn grain as an energy source when formulating diets for high-producing dairy cows.