Achievement of improved reproductive performance in most domestic sheep breeds of the United States has been regarded with considerablecaution because of low heritabilities for reproductive traits. However, this view is changing with increasing availability of exotic breeds that have high reproductive capacity. The characterization of these exotic breeds in crosses with domestic breeds has shown that major improvement in reproductive rate is attainable. Crossbreeding has been demonstrated to be an effective method for exploiting the commercial value of highly prolific breeds (Turner, 1969; Carter, 1976; Dickerson, 1977; Jakubec, 1977; Meyer et al., 1977). The development of composite breeds that combine the potential for greatly increased reproductive rate along with the desired growth, carcass and fleece attributes is an important extension from crossbreeding for achieving important and permanent increases in production efficiency (Carter, 1976; Smith et al., 1979; Hulet et al.,1981).