Fertilized sheep and cattle ova have not been reported to develop readily during culture in vitro . Up to 60% of sheep morulae develop normally during culture (Moor & Cragle, 1971) but earlier cleavage stages undergo limited development (Hancock, 1963; Kraemer, 1966; Tervit & McDonald, 1969; Moore, 1970) and it has been suggested that there is a block to development in vitro at the eight- to twelve-cell stage (Wintenberger, Dauzier & Thibault, 1953). Only the early cleavage stages of cattle ova have been cultured and these have not been reported to develop beyond the twenty-four-cell stage in vitro (Thibault, 1966; Brinster, 1968; Sreenan, 1968; Sreenan, Scanlon & Gordon, 1968). This communication describes the successful culture of one-cell to eight-cell sheep ova and one-cell and eight-cell cattle ova to the morula and blastocyst stages and reports a high embryo survival after transfer of cultured ova to recipient animals.

Welsh mountain ewes were induced to superovulate and were mated at the