Horse embryos can be transferred to the recipient mare’s uterus in the
medium in which they were recovered. However, it is more usual to
transfer the embryo in a ‘holding medium’ to which it has been moved via a
series of ‘washes’. The holding medium is a better environment for the
embryo in case of any delay in performing the transfer, while the washing
steps help dilute out any microorganisms either introduced during embryo
recovery or already present in the uterus of the donor mare; it is not
uncommon to recover an embryo from an obviously infected uterus.
Transcervical transfer of an embryo is usually performed using a “cassou”
type transfer pipette, after loading the embryo into either a 0.25ml or 0.5ml
straw. The choice of straw size and pipette type is largely a question of
operator preference, but is also influenced by embryo size; small embryos
are easier to pick up in a 0.25ml straw, but large embryos may not fit into
the straw or out of the pipette opening (Jasko 2002). Aternat ively, horse
embryos (in particular large ones) can be transferred using a sterile
insemination pipette (Wilsher and Allen 2004). In all cases, the straw is
loaded with three columns of fluid separated by air spaces, with the
embryo in the second column; the first fluid column serves to lubricate the
pipette exit, while the third ensures that the embryo is flushed out of, and
away from, the pipette.
The exact technique used to manipulate the transfer pipette through the
cervix and into the uterus differs between operators. Nevertheless, the
essentials are to ensure that the pipette enters the uterus without the
accompaniment of contaminants picked up from the recipient’s vulva or
vagina, and with minimal trauma to the cervical canal and endometrium.
Contamination is minimized by enclosing the pipette in a sterile plastic
sheath (‘chemise’) within which it is introduced into the external os of the
cervix. Once in the cervix, the sheath is pulled slowly but firmly backwards
while the pipette is maintained in place, such that the sheath tears and the
sterile pipette alone is advanced through the cranial portion of the cervix
and into the uterine lumen. Besides tearing the chemise at the correct
moment, the dexterity required for transcervical ET is the ability to
manoeuvre the pipette through the constricted cervical canal without
excessive dilation or trauma; this manipulation can be facilitated by
grasping the protruding portion of the cervix firmly between two fingers and
pulling it backwards so that it straightens. Alternatively, Wilsher and Allen
(2004) have described the use of a duck-billed speculum to visualize, and
a modified rat-toothed Velsellum forceps to grasp and straighten, the
cervix; this has the same overall effect as the manipulation described
above but requires less dexterity, although it does involve more operators.
Transrectal palpation to direct the transfer pipette further into a uterine
horn is probably unnecessary, but may be helpful if there doubts as to
whether the pipette has passed through the internal cervical os and into
the uterine lumen.
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
132