The case of the lost marbles
A routine exam reveals extensive uterine damage that resulted from a popular method to control estrus.
It was time for a change. Delia, an
8-year-old Quarter Horse mare,
had been successful in the show
ring as a Western Pleasure horse,
but now her owners were looking for-
ward to breeding her and raising a foal.
Their first step was to schedule a veteri-
nary examination to ensure she was in
good health.
“An exam is always a good idea
before breeding a mare,” says Regina
Turner, VMD, PhD, of the University
of Pennsylvania’s New Bolton Center.
“Usually, they turn up nothing remark-
able in a younger, maiden mare.”
During the exam, Delia’s veterinar-
ian inserted a transrectal ultrasound
probe to take a look at the mare’s uter-
us. When it’s empty, the equine uterus
is small---you could cup it in your hand
---so it doesn’t take long to scan the
entire organ.
“On ultrasound, the uterus should
look all gray,” says Turner. “But this
veterinarian saw a bright, white cir-
cle, created by something spherical
and dense enough that the ultrasound
waves didn’t pass through it but instead
bounced right off.”
Then the veterinarian noticed a
second strange shape in Delia’s uterus.
This appeared to be another solid ob-
ject, with at least one flattened, irregu-
lar surface. She removed the ultrasound
probe and attempted to feel inside the
mare’s uterus with her hand. A mare’s
cervix, the opening to the uterus, can
typically be penetrated with a single
finger and carefully dilated manually
to allow some access to the space.
But on Delia’s cervix, the veterinar-
ian could feel only a mass of fibrous
scar tissue, which effectively sealed the
opening shut.
These findings all pointed toward
one scenario: Delia, the veterinarian
said, most likely had a marble in her
uterus and possibly a second, which
had shattered.
Over the past decade, marbles have
become popular for controlling estrus
in mares. The small glass balls are
sterilized and placed in-
side the uterus in an at-
tempt to mimic an early
pregnancy, “tricking”
the mare’s body into
behaving as if she’s in
in no more than 40 percent of mares for
an average of 90 days. Still, this method
of controlling a mare’s cycle is appeal-
ing, especially to owners of horses in
competition, because it does not re-
quire drugs and can be reversed after
removing the marble.
Delia’s owners had not placed
marbles in their mare. But when her
previous owners were contacted, they
confirmed that they had indeed placed
one marble in, and then they added a
second when the mare began to cycle
again. “The previous owners probably
assumed the first marble had been
expelled,” says Turner, “but from the
looks of the ultrasound, it hadn’t.”
Inside the mare the two marbles
had most likely struck each other re-
peatedly, causing one to crack and
eventually break into pieces. Delia’s vet-
erinarian believed that the irregularly
shaped object she’d seen on the ultra-
sound was probably a piece of the dam-
aged marble, and the scarring of the
cervix had resulted from injury caused
when the uterus attempted to expel the
sharp glass shards. Remarkably, Delia
had never shown any signs of discom-
fort or discharge.
Still, this diagnosis was speculative.
Unable to access the mare’s uterus to