Blastocysts were collected non-surgically from 2 Przewalski's horse and 2 Grant's zebra mares and transferred extra-specifically to domestic horse and donkey recipients. Nine Przewalski's horse embryos were transferred surgically, and 2 non-surgically, to domestic Welsh-type pony mares. After surgical transfer, 7 (77.8%) pregnancies were established and 4 foals were born. Twelve Grant's zebra embryos were transferred surgically to 5 pony and 7 domestic donkey recipients respectively and 1 non-surgically to a donkey; 3 (60%) zebra-in-horse pregnancies were established and 2 went to term. Only 2 (28.6%) zebra-in-donkey pregnancies were established but neither went to term, although one zebra foal was aborted alive at Day 292 but failed to survive. No pregnancies resulted from the non-surgical transfers. Measurement of chorionic gonadotrophin concentrations and parental-specific lymphocytotoxic antibodies in the serum of the recipient animals indicated a pronounced maternal immunological response to the extra-specific embryo, but this could not be correlated with success or failure of pregnancy. The results indicate that extra-specific embryo transfer may be a useful aid to breeding exotic equids in captivity.
Summary A total of 43 non‐surgical embryo recoveries performed on two Przewalski's horse mares (Equus przewalski) and two Grant's zebra mares (E burchelli) yielded 11 Przewalski and 14 zebra embryos. Surgical transfer of nine Przewalski embryos to domestic pony recipient mares resulted in seven (78 per cent) extraspecific pregnancies. Two of these recipient mares gave birth to live foals on Days 324 and 329 of gestation respectively and two are at Days 175 and 166 respectively at the time of writing; three conceptuses were resorbed at various times between Days 20 and 100. Non‐surgical transfer of two Przewalski's horse embryos and flank surgical transfer of one other Przewalski's horse embryo to domestic mares failed to establish any pregnancy. Surgical transfer of five zebra embryos to domestic pony recipients resulted in three (60 per cent) extraspecific pregnancies; one conceptus was resorbed between Days 61 and 70 and the other two are at Days 190 and 201 respectively at the time of writing. Surgical transfer of seven zebra embryos to jenny donkeys gave two (29 per cent) extraspecific pregnancies; one conceptus was resorbed between Days 53 and 79 and the other foal was born prematurely on Day 292 and lived for only 3 h. Non‐surgical transfer of one Day 10 zebra embryo to a jenny donkey did not result in a pregnancy. These experiments demonstrated that it is possible repeatedly to recover embryos non‐surgically from sedated wild equids and transfer them successfully to domestic horse and donkey recipients. The production of such extraspecific pregnancies by embryo transfer has considerable value as a research tool and the technique should also prove valuable in the future for maximising the reproductive potential of endangered equine species in captivity.
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