Pelleted commercial concentrate feeds containing 0, 3 and 6% of liquid Streptomyces solubles (LSS) and 18% crude protein (CP) were fed as pasture supplements to Holstein and Brown Swiss cows in a 3x3 Latin square experiment, replicated 4 times, and with 3-week comparison periods. To simulate conditions of time limited to that spent in the milking parlor for consuming concentrates, as practiced on many local farms, the animals had individual free access to their respective concentrates for exactly 7.5 minutes twice daily. Twelve experimental cows grazed rotationally at 4/ha in six 0.5-ha paddocks of abundant gramineous herbage that analyzed 7.06% CP. Means observed with supplements containing 0, 3 and 6% LSS: daily production of milk, 15.4, 15.5 and 15.9 kg; 4% fat-corrected-milk (FCM), 13.8, 13.4 and 13.7 kg; percentage milk fat, 3.33, 3.07 and 3.10; and solids-not-fat, 8.33, 8.29 and 8.36; daily concentrate intake, 7.67, 7.30 and 7.03 kg; rate of eating concentrate, 0.511, 0.487 and 0.469 kg/min; ratio of FCM/concentrate dry matter, 1.85, 1.87 and 2.01 kg/kg; daily change in live weight, 0.191, -0.006 and 0.161 kg. Consumption of the control concentrate exceeded (P<0.05) that of the two LSS-containing concentrates combined. Other treatment effects were not significant. Addition of the present levels of LSS to the concentrates was compatible with maintaining both pellet quality and animal performance normal. Therefore, LSS seems suitable for use in this manner. Another important conclusion is that sufficient concentrate was consumed in 15 minutes daily to adequately supplement grazed herbage at these levels of milk production.