Production of ovine chimeras by inner cell mass transplantation.

Ovine chimeras were produced by micro-injection of isolated inner cell masses (ICM) into recipient blastocysts. Inner cell masses were isolated by immunosurgery. A total of 57 chimeric embryos was produced, 52 of which were transferred to recipient ewes. Thirty-seven live lambs were born, of which 15 were determined to be chimeric on the basis of blood type analysis. One lamb, although not a blood chimera, exhibited overt signs of chimerism. An additional six lambs were determined to have developed solely from the injected ICM. The rate of chimerism in live lambs was 43% (16/37) while the survival rate of injected ICM was 59% (22/37). The method presented allows the production of relatively large proportion of viable, chimeric embryos without the use of an intermediate recipient.