Determining the sex of fetal in the mare
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This article explains how they can now determine the sex of
the foal in the mare
Fetal Sex Determination in the Mare
between 90 and 150 Days
Accurate determination of fetal sex can have a profound impact
on the broodmare management practices of horse owners and
breeders. While the gender of a foal influences its value, it
also influences the value of the gravid (pregnant) mare.
Knowing fetal sex prior to foaling allows horse owners and
breeders to make timely, informed management decisions,
including those related to foaling location and subsequent
mating of the mare. Demand for equine fetal sex determination
among horse owners has risen significantly in the past decade,
and it will likely continue to increase.
Richard Holder, DVM, of Hagyard Equine Medical Institute in
Lexington, Ky., described ultrasonographic techniques used to
determine fetal sex at various stages of gestation, focusing
primarily on those employed between 90 and 150 days. He
characterized what can be viewed at different stages of
pregnancy during his presentation at the Hagyard Bluegrass
Equine Symposium 2006, which was held October 18-21 in
Lexington.
Using transrectal ultrasonography, the skilled veterinarian can
accurately determine equine fetal sex after 54 to 55 days of
gestation. Between Days 55 and 90, fetal sex determination is
possible in 95% of initial exams, with 99% accuracy. At that
stage of the mare's pregnancy, the veterinarian must first
locate the fetal genital tubercle, a structure that will
ultimately form the penis in the male and the clitoris in the
female.
At 80 to 90 days of gestation, the sex of the fetus becomes
more difficult to assess due to the position of the uterus in
the posterior abdomen.
"At approximately 80 days, the fluid of the pregnancy begins to
pull the uterus over the rim of the pelvis into the abdominal
cavity, which makes it harder to find," explained Holder.
Later, as the uterine contents increase in size, the elevated
uterus is more accessible. Between 90 and 150 days of
gestation, a second technique is required to determine fetal
sex using transrectal ultrasonography. The examination involves
locating the gonads and the external genitalia of the fetus in
the male that includes the penis, glans penis, and prepuce.
Identifiable in the female are the gonads, mammary glands,
teats, and clitoris. With a single examination performed at 90
to 150 days of gestation, the skilled veterinarian can
determine fetal sex on initial exam in 90% of cases with 99%
accuracy.
Around 150 days of gestation, the fetus begins to assume an
anterior presentation. In this position, the fetal head is
easily accessible, while the pelvic area is beyond the
veterinarian's reach. Between 150 to 200 days of gestation,
determination of fetal sex using transrectal ultrasonographiy
is difficult, and the likelihood of making an accurate
diagnosis falls to 10-25%.
At that stage of gestation, a transabdominal (viewing through
the belly) ultrasonographic examination typically is required
to identify the external fetal genitalia. For greater ease and
accuracy of fetal sex determination, Holder recommended the use
of transrectal ultrasonographic techniques earlier in
gestation.
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