Summary In three experiments, 86 Jerseys and 17 Holsteins were used in a study of the effects of rumen inoculations, chlortetracycline and other feed supplements, on growth and digestion of calves fed high roughage pellets. The effect of feeding high roughage pellets of different composition, and of rumen inoculations, on establishment of rumen microorganisms, rumen volatile fatty acids, artificial rumen digestion, and rumen pH are presented in a companion paper. The feeding of high roughage pellets (basically, two parts one-half inches ground alfalfa hay and one part a simple grain mixture made into pellets one-fourth inches in diameter) resulted in earlier dry feed intake, earlier rumen function, and more rapid growth than was observed in previous experiments, in which loose hay and grain were fed separately in a 2:1 ratio. Growth and feed intake were enhanced when chlortetracycline was included in the pellets. Little effect was observed when chlortetracycline was fed in the milk to 7 wk., then administered by mixing in 1lb. of warm water from 7 to 16 wk. No benefit was observed from the combined effects of adding molasses, distillers solubles, calcium phosphate, and brewers yeast to the basal high roughage pellets in two experiments. Reducing the total protein of the basal high roughage pellets from 14.3 to 12.3% by replacing all of the soybean meal with corn resulted in retarded growth and lower feed intake in both Jerseys and Holsteins. Replacing approximately one-half the alfalfa hay with good timothy hay in the basal pellets had no appreciable effect on growth or feed consumption, despite somewhat lower digestibility of dry matter and cellulose in the pellets that contained timothy hay. No significant differences in the performance of rumen-inoculated calves compared to uninoculated calves were measured. There was a tendency, though the differences were not statistically significant, for the uninoculated calves to perform better than those that were inoculated. Rumen (cud) inoculation in relation to the high roughage system for raising calves is discussed.