Summary Twenty high producing dairy cows were divided into four experimental groups consisting of three Holsteins, one Jersey and one Guernsey per group. Three rates of grain replacement (15, 30 and 45 per cent) with a commercially dehydrated grass-legume mixture were studied a total of 28 wk., using 6-wk. experimental periods and 1 wk. for transition for each group of cows for each ration. The following results were observed: (a) Cows, when fed the control ration, gained an average of 25.7 lb. in body weight per cow per period, as compared with 16.8, 18.6 and 8.5 lb. when they had 15, 30 and 45 per cent, respectively, of their grain replaced with dehydrated grass. (b) A digestion trial with three sheep showed that the commercially dehydrated material used contained 66.8 per cent total digestible nutrients on an air-dry basis. (c) Cows fed the control ration produced an average of 36.8 lb. of 4 per cent fat-corrected milk daily, compared with 35.5, 35.3 and 35.7 lb. when they had 15, 30 and 45 per cent of their ration replaced with dehydrated grass, respectively. This difference in production in favor of the control ration was statistically significant. (d) The finely ground physical state of the dehydrated grass-legume mixture was undesirable, since cows having 30 and 45 per cent of their grain replaced showed varying degrees of rumen atony and anorexia. This condition was not observed when the cows were on the control and 15 per cent rations. (e) Cows receiving no dehydrated grass required less total digestible nutrients for maintenance and production of 100 lb. of 4 per cent fat-corrected milk than when they received dehydrated grass. (f) The rate of decline in milk yield was less rapid when the cows were fed the control ration, but these mean differences only approached significance.