Page 454 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 429

VetBooks.ir with the recipient mare ovulating 1–3 days after 2.28
the donor. The donor mare is mated as previously
described by natural cover or AI during oestrus. The
embryos are collected between days 6 and 10 post
ovulation. Chilled semen inseminated mares are
usually flushed on day 7 and frozen semen insemi-
nated mares on day 8 post ovulation as this enhances
the chances of collecting an embryo from within
the uterus. In addition, it is a size that can be easily
manipulated and transferred to the recipient mare
while minimising any trauma to the embryo. The
flush is performed in a sterile fashion with the mare
restrained in stocks (sedation may be necessary) and
the perineum prepared as described for AI insemi-
nation. The closed flush system involves a Bivona
foley catheter and Y-tubing attached to the flushing
medium and an embryo filter. The foley catheter is
inserted into the uterus through the closed cervix and
the inflatable cuff filled with 50–80 ml of flushing
medium. The uterus is distended with the flushing
medium until both horns are distended, which may
be mildly uncomfortable for the mare. The volume Fig. 2.28 Collection of embryos from a donor mare
used ranges from 500 to 3000 ml depending on the via uterine lavage. (Photo courtesy Tracey Chenier)
type of mare. The fluid is then drained via a sterile
container through a 75 µm embryo filter (Fig. 2.28). 2.29
This process is repeated 3–4 times and accompanied
by rectal massage of the uterus to encourage further
collection of any embryos still present. Transrectal
ultrasound is used to ensure all flushing medium has
been removed. The embryos are recovered from the
filter by rinsing with flushing solution into a grid-
ded search dish. Embryos are identified using a dis-
secting microscope (7–10 × magnification) and then
washed with flushing and holding solutions before
transfer into a special holding medium in which they
are graded microscopically for quality, viability and
freedom from abnormalities (Fig. 2.29). Embryos
can remain viable for up to 24 hours at 5°C (41°F) Fig. 2.29 Blastocyst embryo day 8 post ovulation
within a holding medium in a passive cooling device, under high-power magnification.
but where possible the interval between identifica-
tion and transfer should be minimised, preferably to mares have lower collection rates due to poorer fer-
less than 60 minutes. If no embryos are found, it is tilisation rates and high embryonic loss before day 6;
possible to place a further 2 litres of flushing solu- semen quality of the stallion; single ovulating mares
tion into the mare’s uterus and, before re-collection, only have 50% recovery per cycle.
administer oxytocin. Embryo recovery rates can Recipient mares should be healthy, free from
vary and several factors have been identified: days any reproductive problems of their own, cycling
7–9 collection is more efficient than day 6; older normally and preferably young (3–8 years old).