Effects of chimerism in sheep-goat concepti that developed from blastomere-aggregation embryos

Chimeric sheep-goat pregnancies were established in 24 ewes and 29 does by transferring 251 embryos, prepared by the blastomere-aggregation technique, to 52 ewes and 61 does. Fifteen does experienced early pregnancy failure; however, term offspring were delivered by 24 ewes (17 lambs, 3 kids, 6 chimeras) and 14 does (6 lambs, 9 kids, 6 chimeras). (Fetal classifications were based on phenotype, red blood cell isozymes, and lymphocyte antigen expression). RIAs for ovine and caprine placental lactogen detected chimerism in the binucleate cell population of the trophoblast throughout the pregnancies of 2 ewes and 7 does; these pregnancies resulted in the birth of 12 healthy offspring. Histological examinations of intact placentomes from 2 of these recipients revealed a continuous cellular trophoblast apposed to a syncytium as in normal placentas. Chimerism was detected electrophoretically in the membranes of the placentas with binucleate cell chimerism and in 17/28 of the other placentas. Data collected on placental lactogen production, chimerism in the conceptus, and placental morphometry were examined with respect to the stages of the blastomeres aggregated to form the chimeric embryo and with respect to fetal status at delivery. For comparison, analogous data were collected on sheep-goat concepti that developed from embryos prepared by inner cell mass transplantation.