Page 457 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

432 CHAPTER 2

VetBooks.ir of oestrone sulphate (produced by the fetoplacental Rectal examination
This is probably the most frequently used method
unit) can also be used as an indicator of pregnancy
and fetal viability, since it is only produced in the
with transrectal ultrasound examination. It does
presence of a viable fetus. Oestrone sulphate assays for pregnancy diagnosis and is usually combined
can be used from days 60–70 onwards. carry risks to the mare and veterinarian, depends for
its accuracy on the skill of the palpator (particularly
PREGNANCY DIAGNOSIS IN THE MARE in early pregnancy) and is not applicable to small
mares. The main findings are noted in Table 2.1 and
This is an important part of stud farm and individ- particularly concern changes in uterine tone and
ual mare management. There are various techniques enlargement.
available, all of which have advantages and disad-
vantages, and are best used at various stages of the Vaginal examination
pregnancy. Establishing that a mare has a normal Direct vaginal examination and viewing of the cer-
pregnancy is essential, as early embryonic death is vix is no longer considered a safe way of confirming
common in the mare and leads to a wasted breeding pregnancy as it risks introducing bacteria into the
season. Diagnosis of a twin pregnancy, particularly internal reproductive tract or causing inflammation,
early enough to allow positive action, is a vital func- both of which can lead to prostaglandin release,
tion of the equine stud farm veterinarian. luteolysis and pregnancy failure.

Absence of oestrous behaviour Ultrasound examination
Lack of detection of oestrus 16–22 days post ovula- This technique has become established as the most
tion and following insemination is an indirect test important technique for the diagnosis and assessment
for pregnancy. Unfortunately, not all mares that fail of pregnancy in the mare. It is used at the same time
to exhibit oestrous behaviour are pregnant. Other as a rectal examination and therefore has that tech-
reasons include: early embryonic death; retained nique’s inherent risks. It is able to detect pregnancy
CL; silent or poorly shown oestrus; variability in very early on (even as early as day 10 in experimental
the oestrous cycle timing; lactational anoestrus; and situations with some ultrasound machines) and also
teasing at the incorrect time in relation to the true to investigate problems of the reproductive tract.
date of the last ovulation. In addition, some pregnant Ultrasound examination at days 12–16 post ovula-
mares show oestrous behaviour. tion is used most effectively to manage mares that

Table 2.1 Main findings on rectal examination of a pregnant mare
GESTATION UTERINE TONE UTERINE SWELLING CERVICAL FINDINGS
16–19 days Good, firm/turgid Mild swelling Closed tight
20–24 days Good, firm/turgid Ventral bulge at uterine bifurcation Narrow and elongated
30 days Good, firm/turgid Increasing pregnant horn ventral enlargement Closed tight
31–50 days Decreases in pregnant horn. Still Continuing increase in size of bulge. Towards end of period Closed
good in non-pregnant horn starts to include mid-uterine horn and uterine body
51–70 days Decreases in pregnant horn. Still Fluid-filled swelling pregnant horn, body, and some Closed
good in non-pregnant horn distension non-pregnant horn
71 + days Uterus increases in size and moves ventrally. Ovaries Closed
start to move closer together. Ballottement of the fetus
is possible later in pregnancy (>120 days). Palpation
and sizing of fetus may allow ageing by comparison
with breed standards