rectum to ensure that the entire lumen is flushed, and to encourage the
embryo out from under any uterine folds and into the medium, which is
then recovered by gravity flow. While there are many different types of
flushing system in use, most operators employ a closed system with a
central Y-piece, such that flushing medium can flow into the uterine
catheter through one line and, after opening or shutting of clamps on the
appropriate lines, out via a different set of tubing and on through an inline
embryo filter. A combination of per rectum massage and elevation of the
uterus combined with manipulation of the position of the inflated cuff will
usually help maintain a steady outward flow of medium conducive to
embryo recovery. Uterine lavage is usually repeated 3 or 4 times in close
succession, and some operators allow the medium from the last flush to sit
in the uterus for around 3 minutes (Hinrichs 1990), or administer oxytocin
to stimulate uterine contractions (McCue et al. 2003), before beginning
recovery; these procedures may reduce the risk of failing to recover an
intrauterine embryo.
Identification and assessment of the embryo
The bulk of the flushing medium is allowed to pass through the embryo
filter; the final approximately 50ml is retained to search for embryos. At
around 0.5 - 1mm in diameter, a normal day 8 embryo should be visible to
the naked eye. Nevertheless, a dissecting microscope with a magnification
range of x10-x50 will usually be required to locate an embryo on day 7 or
earlier (day 6 embryos start at around 150 mm in diameter) and should
always be used in case the embryo is developmentally retarded, or a
smaller embryo from an asynchronous additional ovulation is also present.
Magnification will also enable examination of the embryo’s quality (grade
1-4; excellent-degenerate: McKinnon and Squires 1988) and
developmental stage (late morula, early blastocyst, expanded blastocyst).
In the case of failed fertilization, the unfertilized oocyte (UFO) is normally
retained in the oviduct (Betteridge and Mitchell 1972) and will not,
therefore, be recovered. On the occasions that a UFO is found, it is
generally assumed to be from an earlier cycle and to have accompanied
an embryo on its passage into the uterus; these UFOs can be
distinguished from viable embryos by their flatter, acellular and more
granular appearance. Importantly, if only a UFO is found, the filter and
searching dish should be rechecked carefully to locate the ‘missing’
embryo.
Transcervical transfer of horse embryos
Until relatively recently, transfer of horse embryos was routinely performed
surgically via either a ventral midline laparotomy under general
anaesthesia (Allen 1982) or through the flank using local infiltration
anesthesia in the standing, sedated mare (Squires et al. 1985). However,
dramatic improvements in the success of transcervical transfer have
rendered surgical transfer largely obsolete; transcervical transfer is
quicker, cheaper and better for the recipient’s welfare; indeed, in some
European countries surgical transfer is banned. Moreover, experienced
operators can routinely achieve pregnancy rates exceeding 80% if suitable
recipients are available (Losinno et al. 2001; Jasko 2002).
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February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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