Page 458 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 433

VetBooks.ir 2.32 2.33

Fig. 2.32 Transverse transrectal
ultrasonographic image of a
single 13-day-old conceptus.
(Photo courtesy Tracey Chenier)

Fig. 2.33 Transverse transrectal
ultrasonographic image of a single
15-day-old conceptus. (Photo courtesy
Tracey Chenier)

present with twin embryos. The timing of the first 2.34
pregnancy scan can vary considerably depending on
the management and breed of the mare, but should
ideally be done 14–16 days post ovulation (if known)
or 16 days from the last breeding. Early-pregnancy
ultrasound examination requires careful, systematic
use of a linear array 7.5 MHz transducer. The main
characteristics of the conceptus are described below:

• Days 10–16. At day 10, small spherical vesicles
are found most frequently in the uterine body,
although they can be found from the tip of a
uterine horn to just cranial to the internal os Fig. 2.34
of the cervix. Great care should be taken to A 19-day
examine the entire uterus as the embryo at this (from
time is very mobile. At day 16, the spherical ovulation)
vesicles are usually found at the caudal portion pregnancy
of one of the uterine horns. During these ultrasound
early days of pregnancy, the rapidly growing scan.
vesicle will have bright echogenic poles (at
the 12 o’clock and 6 o’clock position) that are
not associated with the embryonic disc. The in shape (Fig. 2.34). This is thought to be due
vesicle grows from about 2–3 mm (day 10 from to increased tone and thickness of the uterine
ovulation) to 14 mm (day 14) to about 15–16 mm wall. The embryo is first visualised within the
(day 16) (Figs. 2.32, 2.33). vesicle on day 21, usually in a ventral position
• Days 17–22. The vesicle has a growth plateau (Fig. 2.35). The heart beat is usually detected
between days 17 and 26. After day 17 the vesicle at this time and is used to determine embryonic
is often irregular/triangular or slightly elongated well-being.