Establishment of pregnancy after embryo transfer in mares with gonadal dysgenesis

Embryo transfer was performed in three mares with gonadal dysgenesis. Karyotypes of the mares were as follows: Mare 1, 63,XX, 64,XX, 65,XX; Mare 2, 63,X; and Mare 3, 65,XXX. The mares were administered progesterone in oil, 300 mg intramuscularly daily, starting 1 or 2 days after donor mare ovulation. Embryos were transferred on day 7 after donor ovulation. Mare 1 became pregnant after the first embryo transfer and had a normally developing fetus on necropsy on day 45 of gestation. Mare 3 became pregnant after the third embryo transfer, but the embryo was lost between day 14 and day 18 of gestation. Mare 2 received embryos on six occasions without maintaining pregnancy after transfer. Mares with gonadal dysgenesis treated with progesterone can establish and maintain pregnancy after embryo transfer, but there may be differences in this capability among mares, possibly related to the cause of the gonadal dysgenesis.