Advanced mare age predisposes to chromosome misalignment on the metaphase II spindle of IVM oocytes. The compromised ability to correctly align chromosomes presumably predisposes to aneuploidy in resulting embryos and thereby contributes to the age-related decline in fertility and increased incidence of early pregnancy loss. The Summary is available in Portuguese - see Supporting Information.
Summary
Background
In vitro embryo production (IVEP) is increasingly popular but data assessing the outcome of transferred embryos are scarce.
Objectives
To determine the likelihood of pregnancy and embryonic loss after transfer of frozen‐thawed IVP embryos and identify factors influencing success.
Study design
Retrospective clinical study.
Methods
Blastocysts (n = 261) were produced from immature oocytes of Warmblood mares (n = 116) by Intracytoplasmic Sperm Injection (ICSI) and in vitro culture, and cryopreserved. Thawed IVP embryos were transferred into recipient mares on day 4, 5 or 6 after ovulation. The influence of donor mare (age, reproductive history), recipient mare (age, reproductive status, management; in‐house vs. outpatient, day post‐ovulation), embryo (interval from ICSI to blastocyst formation) and management factors (season when ovum pickup was performed, year and method of transfer) on likelihood of pregnancy and embryonic loss was examined, and the developmental stage of the IVP embryo at the time of transfer was estimated.
Results
The percentage of mares pregnant 7–10, 23 and 37 days after transfer was 56% (147/261), 49% (129/261), and 48% (124/261), respectively. Development of IVP embryos after transfer equated to day 5 or 6 in vivo embryos. With the exception of year of transfer, none of the factors had an impact on the likelihood of pregnancy or embryonic loss. Nevertheless, the likelihood of pregnancy tended to be lower for IVP embryos from infertile mares or when embryos were transferred into recipient mares on day 6 after ovulation rather than on day 4 or 5. Finally, the diameter of the embryonic vesicle 7 days post transfer was lower for pregnancies that were lost compared to those that were maintained.
Main limitations
Small sample size in some of the donor and recipient mare categories.
Conclusions
Cryopreserved IVP embryos should be transferred into recipient mares on day 4 or 5 after ovulation and a slower rate of post transfer vesicle expansion indicates a higher risk of subsequent embryonic loss
The Summary is available in Portuguese ‐ see Supporting Information
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