Heterosis in crosses of inbred lines of Duroc swine.

B ETWEEN 1938 and 1949 seven different unrelated inbred lines of Duroc swine were developed by the Oklahoma Agricultural Experiment Station in cooperation with the Regional Swine Breeding Laboratory. In sixteen of the twenty-two farrowing seasons from the spring of 1939 through the fall of 1949, both inbred and two-line-cross litters were produced. In some seasons outbred Duroc and three-linecross litters were farrowed. The purpose of the present study was to determine if selection within moderately inbred Duroc lines followed by crossing of these lines resulted in improved performance. If so, its manner of expression and the time at which it was first evident were to be investigated.