respectable and, most importantly, because a much higher percentage of
zygotes can be successfully cultured to the blastocyst stage (20-40%).
Indeed, in a commercial equine IVF program, an average of 0.8
blastocysts per ovum pick-up cycle has been reported (Galli et al, 2007),
which compares favourably to embryo recovery rates from a conventional
(unstimulated) embryo transfer cycle (0.3-0.8; depending on semen type).
On the other hand, while initial pregnancy rates following transfer of IVP
blastocysts have been promising, early embryonic loss rates appear to be
high, presumably due to the combined effects of in vitro culture and the
fact that many donor mares are aged. In this respect, IVP embryos show
developmental retardation, reduced mitochondrial numbers and energy
production capacity, altered gene expression and high percentages of
chromosomally abnormal, dead and apoptotic cells. In addition, the
blastocyst capsule, a tertiary embryo coat unique to horses and essential
to embryonic survival in vivo, does not develop normally in vitro. In short,
while equine IVP has finally reached the stage at which it is commercially
interesting, there are many challenges to be met with regard to optimizing
the developmental competence of the resulting embryos.
Conclusions
The non-surgical recovery and transfer of horse embryos are
straightforward techniques for which the equipment required is readily
available from numerous suppliers. However, the likelihood of embryo
recovery is affected significantly by donor mare age and fertility, and by
semen quality; it is important that clients are aware of this before
embarking on a potentially frustrating venture to recover embryos from an
ageing mare inseminated with frozen-thawed semen. Acceptable rates of
pregnancy and pregnancy maintenance following non-surgical embryo
transfer depend on donor mare age and fertility (which influence embryo
quality), recipient mare quality (in particular adequate synchronization of
ovulation) and on the ability of the operator to aseptically and
atraumatically pass a transfer pipette through the dioestrous cervix. On the
other hand, because simple and successful systems exist for cooled
transportation of horse embryos, it is possible to make use of recipient
mares and non-surgical transfer expertise at a distant ET centre. In either
case, it is worth bearing in mind that while the future athletic performance
of ET foals may have a large genetic component, environment will also
undoubtedly play an important role and, in this respect, the provision of an
optimal intrauterine environment in the shape of a suitable (size and health
wise) recipient should not be neglected. Superovulation and
cryopreservation are both techniques with considerable potential to
improve the efficiency and flexibility of ET, and while marked
improvements have been made in both fields in recent years, there is still
considerable scope for improvement. Finally, while it is presumed that nonsurgical ET will eventually become an integral final step for establishing
pregnancy after using more advanced laboratory techniques to salvage
fertility or hasten genetic progress, considerable research into the culture
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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