Three commercially prepared rumen cultures and fresh rumen liquor were compared to determine their effect on the rate of gain and efficiency of feed utilization of a) twenty-four steer calves, b) twenty-four two-year old steers in pasture, and c) twelve weanling lambs. Two of the cultures were prepared from the rumen contents of fast and slow gaining steers from experimental feeding tests, the other was a commercial product marketed under the trade name of Ruzyme. / Master of Science