Page 455 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

430 CHAPTER 2

VetBooks.ir 2.30 is sedated and premedicated with flunixin meglu-
mine. The mare is maintained on an oral progesta-
gen from the day of transfer for approximately 50
days. A number of different commercial instruments
are available for transfer of the embryo. Whichever
instrument is used, it must be sterile or covered by
a sterile sheath and it must be inserted through the
cervix with minimal manipulation (Fig. 2.30).

Prognosis
There are a number of factors that affect the suc-
cess of ET. For the recipient mare the factors with
the largest effect are uterine tone just prior to trans-
fer and the previous fertility of the mare. Embryos
Fig. 2.30 Embryo transfer system. Flushing medium collected on days 7 and 8 have the highest transfer
attached via ‘Y’ tubing to the Bivona catheter in the success rate (up to 75%). Chilling embryos before
uterus. The free end of the ‘Y’ tubing will attach to transfer has no effect on pregnancy rates, but
the filter cup in which the embryo will be present freezing embryos does decrease success rates. Day
prior to insemination. 6 embryos seem to be the best for freezing. The
shorter the time between collection and implanta-
Non-surgical transfer of the embryo into the uterus tion, the more favourable the prognosis. The inci-
of the recipient mare is now the most commonly dence of embryonic death post transfer between
used technique for transfer, and can have similar days 12 and 50 can be up to 15–20% and is increased
success rates (up to 75%) to the more complex sur- by recipient mares >7 days post ovulation and by
gical implantation techniques. The recipient mare poor quality embryos.

THE PREGNANT MARE

MATERNAL RECOGNITION • Secretion by the embryo of antiluteolysins/
OF PREGNANCY luteotropic substances, which are taken up by the
endometrium. The exact nature of these is not
The first maternal recognition of pregnancy is fully known.
thought to occur at about 48 hours post fertilisation
with the production of a protein called ‘early preg- ENDOCRINOLOGY AND MAINTENANCE
nancy factor’ (EPF). This protein has been detected OF PREGNANCY (Fig. 2.31)
in horses, humans, sheep and mice. It may prove
useful in the future for detecting early pregnancy. Progesterone
The embryo enters the uterus at around 5.5–6 days This hormone is essential for the maintenance of
post ovulation. At this stage the embryo is either pregnancy. The primary CL is present following the
a late-stage morula or an early-stage blastocyst. ovulation that led to the pregnancy. The primary CL
Maternal recognition of pregnancy prevents the persists because of the inhibition of PGF α secre-
2
production of PGF α. It is thought to involve: tion described above. After days 35–40 of pregnancy,
2
additional follicles on both ovaries lead to secondary
• Movement of the embryo around the uterus CL (stimulated by equine chorionic gonadatropin,
allowing the embryo to contact every part of the eCG), which form following ovulation of the devel-
endometrium. oping secondary follicles or luteinisation of follicles