Abstract THE efficiency with which a growing animal uses its feed is usually expressed either as the ratio of the gain in live weight to the weight of feed consumed or as the ratio of the weight of feed consumed to the gain in live weight. That is to say, the efficiency of feed utilization is usually measured either by the gain made per unit weight of feed consumed or by the feed required per unit weight of gain made. Inasmuch as the one ratio is the reciprocal of the other, it is obvious that both of them should not be referred to as “efficiencies.” Fortunately, there is a growing tendency to refer to the second ratio (namely, feed per unit weight of gain) as “feed conversion.” The writers urge that the first ratio (namely, gain per unit weight of feed) be referred to as “efficiency of feed utilization” or as …