Page 470 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 445

VetBooks.ir 2.52 • Post-fixation (17–30 days). Bilateral twins
should be manually reduced as described
above. In unilateral cases reduction can be
attempted while the vesicles are small and
there is some separation; however, as they
grow damage may occur to the remaining twin
and further attempts to reduce them should
not be made. Frequent monitoring of unilateral
twins will identify if one will reduce naturally.
Up to 35 days the CL is responsive to
prostaglandin (after 35 days eCG is produced
from the endometrial cups), and if there has
not been a natural reduction of the twin
pregnancy by this time, then prostaglandin
can be given to return the mare to oestrus and
re-breeding.
• Post fixation (30–45 days) Twins identified or left
until this stage should be reduced by repeated,
in-situ gentle trauma directly to the twin to
be reduced using the ultrasound probe until
echogenic material is seen within the vesicle
(a ‘snowflake’ effect). Repeated monitoring is
Fig. 2.52 Twin pregnancy. Two pregnancies (13 days
and 14 days) adjacent to each other in the same uterine necessary to ensure the pregnancy reduces to a
horn. singleton.
Other methods of twin reduction:
embryos will grow and change shape, move around
the uterus prior to 16 days and are thinner walled. • Transvaginal ultrasound-guided twin puncture
is a specialist technique to aspirate allantoic/
Management yolk sac fluid from the fetus. This is ideally
Multiple techniques exist for the management of performed prior to 45 days, as success rates
twins depending on the time they are identified. All decrease after this time.
examinations should be performed in a safe fashion, • Transabdominal ultrasound-guided twin
ideally in stocks to avoid mare movement. Sedation injection is a specialist technique to inject
or muscle relaxants may be required to facilitate this potassium chloride or procaine penicillin into
procedure (using an α agonist such as detomidine) the fetus between 110 and 130 days.
2
and care is required to prevent injury to the mare. • Craniocervical dislocation is a specialist
technique to dislocate/decapitate a twin between
• Pre-fixation (<16 days post ovulation). This is 55 and 110 days via a transrectal manual
the ideal time as the embryos are still mobile and approach or a standing flank laparotomy.
small. The smallest vesicle is identified and moved
away from the other vesicle by applying pressure In all cases of late twin reduction, repeat exami-
from the ultrasound probe, with care being taken nations are necessary to ensure the success of the
to avoid damaging the remaining vesicle. The reduction and assess the risk of both pregnancies
small vesicle should be moved to the tip of the failing. The use of flunixin meglumine at the time of
uterine horn and pressure applied until the vesicle the procedure and progestagen (altrenogest) follow-
is seen to decompress. A slight ‘pop’ may be felt. ing on is appropriate.