D. G. Whittingham

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

Mouse embryos survived freezing to -196 degrees C. Survival required slow cooling (0.3 degrees to 2 degrees C per minute) and slow warming (4 degrees to 25 degrees C per minute). Depending on the specific rates used, 50 to 70 percent of more than 2500 frozen and thawed early embryos developed into blastocysts in culture after storage at -196 degrees C for up to 8 days. When approximately 1000 of the survivors, including some frozen to -269 degrees C (4 degrees K), were transferred into foster mothers, 65 percent of the recipients became pregnant. More than 40 percent of the embryos in these pregnant mice gave rise to normal, living full-term fetuses or newborn mice.

Mouse embryos survived freezing to -196°C. Survival required slow cooling (0.3° to 2°C per minute) and slow warming (4° to 25°C per minute). Depending on the specific rates used, 50 to 70 percent of more than 2500 frozen and thawed early embryos developed into blastocysts in culture after storage at -196°C for up to 8 days. When approximately 1000 of the survivors, including some frozen to -269°C (4°K), were transferred into foster mothers, 65 percent of the recipients became pregnant. More than 40 percent of the embryos in these pregnant mice gave rise to normal, living full-term fetuses or newborn mice.