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Twins: A Disease in Mares

Pet Column for the week of September 13, 1999

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Sarah Probst
Information Specialist

Last spring, my aunt, uncle, and 10-year-old cousin Claire, waited in high anticipation for
the birth of their sure-to-be prodigious foal out of their favorite mare, Babe. Unfortunately,
the birth was a disappointment--two small stillborn foals. Fortunately, the mare was fine;
but many times when twin pregnancies are carried that far into term, the effects on the mare
can be devastating to her reproductive health. Twins are so undesirable in mares that some
veterinarians and horse owners refer to the condition as a disease.

"In a normal pregnancy, the foal is surrounded by a diffuse placenta that helps it develop. It
has a full circle of placenta all to itself. When there are twins, the two foals have to share the
space normally allotted for one. The reduced placental surface area isnít enough to give
both fetuses what they need to survive, so one or both are naturally aborted or resorbed,"
says Dr. Ted Lock, retired veterinarian and professor in reproductive physiology at the University
of Illinois College of Veterinary Medicine in Urbana.

"If the mare doesn't naturally abort one or both fetuses, you may need a veterinarian's help
to make sure an advanced twin pregnancy doesn't cause complications that could be
devastating to your mare's fertility," says Dr. Lock.

"In the cases where intervention is needed, it is ideal to detect twin pregnancies before 30
days," says Dr. Lock. "If twins are found, you have a few options."

1.Abort both fetuses and start over. At less than 35 days unwanted fetuses can be
removed by a veterinarian by administering prostaglandin.
2.Have the veterinarian remove one of the fetuses during palpation and allow the other
one to develop. "With race horses, we always try to leave the faster one," jokes Dr.
3.After 45 days, if you would still like to save one of the fetuses, surgical removal of
one may be an option.
4.If the fetuses are really close together, selective abortion is often impossible. Your
veterinarian may be able to do a transvaginal needle aspiration of one of the fetusí
placental fluid. But often if the fetuses are too close, when one is aborted, the other
dies as well.
5.Or you can opt to do nothing, and wait to see if the mare reduces the embryos on
her own. Only 1 percent of twin pregnancies are carried to term. Know that the
hope of two viable foals is dim and could be dangerous to the reproductive health of
your mare.

Many mares have double ovulations. Those that result in twin pregnancies usually resolve
themselves, but it is wise to check. If you want to get the most out of the time you've
invested in your mare's reproductive potential, youíll need your veterinarian's help so you
aren't disappointed by two stillborn foals in the spring.

This season, my aunt and uncle and their veterinarian are monitoring their mare early to
detect possible twins. They recently received confirmation that a single fetus is present and
healthy. The sure-to-be prodigious foal should arrive in May!

For more information, contact you local equine veterinarian.