Successful transfer of day 10 horse embryos: influence of donor–recipient asynchrony on embryo development

Abstract

A total of 78 day 10 horse embryos were transferred non-surgically to recipient mares that had ovulated 9, 7, 6, 5, 4, 3, 2 or 1 day after (negative asynchrony), on the same day (synchronous), or 2 or 4 days before (positive asynchrony) the donor (nZ6 or 8 mares per group). Pregnancy rates between 100% (6/6) and 63% (5/8) were seen in recipient mares that were between C2 and K6 days asynchronous. Embryo survival to the heartbeat stage declined in recipients that were K7 days asynchronous and no embryos survived in recipients that were K9 days asynchronous. Irrespective of uterine asynchrony, cessation of embryo mobility and fixation at the base of a uterine horn occurred when the conceptus was w17 days old. Conceptus growth and development was slowed when embryos were placed in negatively asynchronous uteri. At the greatest degree of negative asynchrony at which embryos survived to the heartbeat stage, i.e. K7 and K6 days, development of the embryo proper and allantois was retarded. Luteostasis was achieved in recipient mares when day 10 embryos were transferred to recipient mares at any stage of asynchrony between K9 and C2 days with respect to the donor. These results indicate that in the horse, there is a wide window for establishment of pregnancy following embryo transfer to asynchronous recipients. Although progesterone priming of the uterus to a stage equivalent to that of the transferred embryo does not appear to be a prerequisite for embryo survival, it does nonetheless influence embryonic development.Reproduction (2010) 139 575-585

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.…”

“…By day 19, vesicle diameter was no longer statistically different, in part because of intra-group variability, but also because this is the period (days 17e27) in which the vesicle loses its perfectly spherical shape and enters the 'plateau phase', when it ceases to show a marked day-today increase in diameter [30]. Nevertheless, the reduced diameters observed by ultrasonography paralleled the developmental delay of approximately four days reported by Wilsher et al [8] after conceptuses were transferred to a six day negatively asynchronous uterus. In the current study, asynchronous embryos also underwent a delay in the processes of gastrulation, neurulation and organogenesis.…”

“…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].…”

Influence of the uterine environment on the development of in vitro-produced equine embryos

“…with an embryo proper), it does illustrate that the uterus should be mechanically capable of retaining embryos introduced soon after ovulation. Wilsher et al 's (2010) study also illustrates the possibilities and limits of embryo-uterine synchrony. Optimal synchronisation between donor and recipient mares yields the best results; it is, however, not known at which stage after ovulation the uterus of a recipient mare is best suited to nourishing embryonic stages that normally develop in the oviduct, especially when development may have been delayed by production in vitro.…”

“…Firstly, it is possible that closure of the cervix 2-3 days after ovulation was suboptimal, and allowed loss of the embryos via the cervix. However, pregnancy after transfer of day 10 embryos to recipient mares on day 1 or 3 after ovulation has been described by Wilsher et al (2010) and, although none of the embryos subsequently developed into normal pregnancies (i.e. with an embryo proper), it does illustrate that the uterus should be mechanically capable of retaining embryos introduced soon after ovulation.…”