Summary. Fourteen horse embryos recovered non-surgically on Days 6\p=n-\8after ovulation (Day 0) were cooled slowly to \m=-\35\s=deg\C(7 embryos) or \m=-\40\s=deg\C(7 embryos) and stored in liquid nitrogen (\m=-\196\s=deg\C) for 4\p=n-\98 days. Surgical transfer of the thawed embryos to unmated recipient mares that had ovulated \m=-\2 to + 1 days with respect to the embryo donors resulted initially in the establishment of 4 conceptuses. However, only one mare maintained her pregnancy to term.

Summary. In-vitro treatment of preimplantation mouse embryos with spermine and spermidine biosynthesis inhibitor, methylglyoxal-bis-(guanylhydrazone) (MGBG)

Control ovine oocytes matured and fertilized in vitro were transferred to intermediate recipient ewes. After 5 days, 59% of eggs were recovered. Thirty-one (38%) reached morula/blastocyst stage. Twenty-one embryos at the morula or blastocyst stage were transferred to six recipient ewes, resulting in five pregnancies, of which four were maintained. Nine lambs were born (43%). In the experiment, 72 ooctyes matured and fertilized in vitro were cocultured for 5 days with sheep oviductal epithelial cells. Thirty-one eggs (43%) developed to the noncompacted morula stage. Transfer of 26 embryos to 11 recipient ewes resulted in two pregnancies (18%). Two male lambs were born. The result indicates that the coculture of in vitro matured and fertilized ovine eggs with sheep oviductal epithelial cells throughout the preimplantation period is compatible with further development to term.

Chromosomal analysis was carried out on blood lymphocytes, skin fibroblasts, and germinal cells of an interspecies goat-sheep chimera. This chimera was produced by aggregation of blastomeres of goat and sheep embryos. A cell chimerism 54,XX/60,XY was found in blood lymphocytes and skin fibroblasts. At birth the percentage of lymphocytes with karyotype 54,XX (sheep) amounted to 80% and with karyotype 60,XY (goat) to 20%. With age the percentage of lymphocytes with chromosome complement 54,XX increased, so that at 18 months it was 94% sheep and 6% goat. At the same age, in skin fibroblasts the percentage of cells with goat karyotype reached 25%. Analysis of germinal cells showed in spermatogonia the presence of only karyotype 60,XY and in primary spermatocytes of 29 autosomal bivalents and the sex bivalent XY.

Summary. Methanol was examined as a cryoprotective additive that permits the direct transfer of frozen\p=n-\thawed Day-4 mouse embryos to foster mothers without dilution of the cryoprotectant. Methanol permeated the embryos rapidly, was not toxic and exerted a cryoprotective action. The highest level of survival (50%) of embryos in vitro was observed after equilibration in Medium PB1 containing 3\m=.\0 M-methanol, slow cooling (0\m=.\5\s=deg\C/mi n) to a temperature between \m=-\30 and \ m=-\40\s=deg\C,rapid cooling (800\s=deg\C/min) and storage in liquid nitrogen ( \m=-\196\s=deg\C), rapid warming (800\s=deg\C/min), and rapid dilution. A high rate of development in vivo to late-stage fetuses (up to 81%) was observed when cryopreserved embryos were transferred to pseudopregnant recipients immediately after thawing.