Effect of embryo age and recipient asynchrony on pregnancy rates in a commercial equine embryo transfer program

Negative uterine asynchrony retards early equine conceptus development and upregulation of placental imprinted genes

“…As in previous studies, early equine embryos transferred to a severely negatively asynchronous uterus were able to adapt and survive without an obvious reduction in their viability, in as much as they were able to establish pregnancy albeit with an obvious retardation in the rate of development [3,8,29]. Moreover, the delay in development was detectable at the level of the transcriptome in that expression of imprinted genes and DNMTs in yolk-sac membrane of conceptuses recovered from an asynchronous uterus was altered, in most cases this involved a reduction presumed to result from delayed upregulation.…”

“…In the horse industry, embryo transfer is a common practice and often, due to shortage of recipients, nonoptimally synchronized recipient mares are used. Good synchrony between a donor and a recipient mare is considered to have been obtained when the recipient ovulates 1 day before to 3 days after the donor [2]; however, increasing the degree of negative asynchrony does not seem to be harmful to the conceptus and could be beneficial in a commercial setup, requiring fewer recipient mares to be available [3].…”

“…One notable exception is the equine conceptus which, although showing a significant retardation in development, can tolerate up to five days of negative uterine asynchrony without a marked loss of viability [3,8].…”

Factors affecting the likelihood of pregnancy and embryonic loss after transfer of cryopreserved in vitro produced equine embryos

“…Based on morphological characteristics, IVP blastocysts have been proposed to correspond most closely to day 5 in vivo embryos or those that are 1 or 2 days delayed in development [11] and it is therefore recommended to transfer IVP embryos into recipient mares with a corpus luteum that is 4, 5 or 6 days old [12]. Nevertheless, because discrepancies in donorrecipient synchrony for flushed, in vivo embryos are less well tolerated in recipient mares that ovulated before rather than after the donor mare [9], we speculate that IVP embryos might benefit from a less advanced uterine environment. Finally, because IVEP can be performed year-round and older mares are often over-represented in clinical IVEP programs, it is imperative to assess the impact of both mare age and time of year at OPU on the likelihood of success.…”

Hormone supplementation protocol using estradiol benzoate and long-acting progesterone is efficient in maintaining pregnancy of anovulatory recipient mares during autumn transitional phase

“…However, this procedure may entail several limitations because the synchrony between donor and recipient is sometimes difficult to achieve and multiple recipients may be required for a donor mare (Jacob et al, 2012). Another problem for this procedure is that the period over which estrous synchrony can be accomplished in recipient mares is very short at the end of breeding season.…”