Preliminary observations on reproduction in a female sheep-goat chimaera

Department of Animal Science, School of Veterinary Medicine, University of California, Davis 95616.

Four oestrous cycles of a female sheep-goat chimaera were monitored by using a vasectomised ram. The mean (+/- se) length of the cycle was 18.5 +/- 0.64 days with a range from 17 to 20 days. The chimaera was superovulated twice, bred to fertile rams, and the embryos recovered by laparotomy 13 or five days after oestrus, so that karyotype analysis could reveal the genotype of the oocyte. After the first superovulation one ovine day-13 embryo was collected; two fragments of another embryo (or embryos) were also collected, but readable chromosome spreads were not obtained from these embryos or from the two four-cell embryos that were collected five days after the second superovulation. Two surgical embryo transfers to the chimaera resulted in pregnancies. The first transfer involved an eight-cell ovine embryo and two caprine morulae and ended in the abortion of an ovine fetus between days 110 and 130. The second pregnancy occurred after the transfer of two ovine and two caprine morulae. A healthy lamb was born on day 147 of pregnancy. Both placentae had small numbers of cotyledons. A histological evaluation of the cotyledons revealed an abnormal placentome structure in the first pregnancy but not in the second.