Shropshires, Columbias, and Hampshires produced 19% more lamb per 100 lb. of ewe when mated to another breed. This increase in productivity was likely due to heterosis and difference in breed size. The Rambouillet ewe was 27% more productive, when used in crossing, than the Shropshire ewe mated to a Shropshire ram. Border Leicester, Hampshire, and Columbia rams sired the fastest growing lambs when mated to Rambouillet ewes. However, the Border Leicester crosses resulted in the largest total productivity and resulted in the greatest advantage over the Purebred and Shropshire matings.