Horse Breeding: Broodmare Care Tips

If you’re considering breeding your mare, it’s important to understand the procedures your veterinarian might perform on your mare during both normal and abnormal breeding cycles.

Normal Cycle

“The very first examination by the veterinarian is usually on the first or second day of heat,” Dr. Michelle LeBlanc says. “The farm is responsible to present the mare at the correct time to the veterinarian.

“That first exam typically consists of a rectal palpation, and I routinely do an ultrasound scan, possibly a vaginal speculum exam and a culture,” she adds.

“In my practice, if I ultrasound the mare and there’s no free fluid in the uterus, and on the speculum exam there’s no discharge, and the cervix is lying on the floor of the vagina and is normal, I might not culture the mare. In many places, the culture is automatically part of that first exam.

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“At that time, you measure the size of the follicles to determine when it’s best to breed the mare,” Dr. LeBlanc continues. “If we’re talking about a breeding from April through June, mares are typically bred either the third or fourth day of heat.

“Either at that point in time, or not until the next day, the mare may get a shot of human chrionic gonadotropin (a hormone produced by women during pregnancy used to artificially induce a mare’s follicle to ovulate) to make her ovulate, and she’ll typically ovulate 36 to 48 hours later.”

Everything is timed so that the mare is bred prior to ovulation. Since the egg dies a few hours after ovulation, the goal is to have the semen in the uterus waiting for the egg.

“If the mare is normal, I will ultrasound her again before breeding, to determine the size and texture of the follicle, and whether or not she’s ovulated. If she ovulated, we won’t breed her.

“At the time the mare is bred, if by artificial insemination, we determine if the cervix is opening properly.”

Dr. LeBlanc ultrasounds the mare again 24 hours post-breeding to verify that the mare ovulated and to see whether there is any fluid in the uterus.

“The most important ultrasound is the one done 24 hours after breeding,” she says. “If there’s free fluid in the uterus then, you’ve got a big problem.”

That fluid indicates the uterus is inflamed and may be infected.

Dr. LeBlanc ultrasounds the mare again 14 to 16 days post-ovulation to check for a pregnancy.

Abnormal Cycle

“With a mare you know is a problem, prior to breeding we would perform a complete reproductive exam,” Dr. LeBlanc explains. “That would be a rectal palpation, an ultrasound, speculum exam, a digital exam of the cervix, a culture and a cytology.

“We would also do a thorough physical exam to determine her reproductive conformation. Is the angle from the anus to the vulva horizontal? Is she pooling urine in the vagina? Are there feces in the vagina? Mares with poor reproductive conformation are very prone to contaminating themselves.”

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The most common problem Dr. LeBlanc finds that mares have during breeding is an inability to clear fluid from the uterus, and it often relates to poor reproductive conformation.

“Problem mares often can’t clear their uterus quickly,” Dr. LeBlanc says. “In those cases, we breed them, and then four to six hours after breeding, we lavage the uterus and follow that with a shot of oxytocin. And we re-evaluate at 24 hours.”

“At 24 hours post-breeding, if we still have fluid, or edema in the uterine wall, I’ll lavage the uterus again. At this point in time, I might infuse antibiotics into the uterus.

“If we breed a mare two cycles and she doesn’t get pregnant, at that point I start all over again with a complete reproductive exam and might also include a uterine biopsy.”

Important Mare Reproduction Terms

• Reproductive Cycle: The hormonal cycle in which a mare prepares her uterus for conception and produces an egg ready for fertilization. It usually lasts 21 days: five to seven days in heat (estrus), under the influence of estrogen; 14 to 17 days out of heat, under the influence of progesterone.
• Ovary: The female reproductive organ that produces eggs; a typical female has two.
• Follicle: The structure of the ovary where an individual egg develops. In a typical reproductive cycle, only one follicle on one ovary matures to produce an egg.
• Ovulate: When a follicle ruptures and releases a mature egg ready for fertilization; the rupture itself is an ovulation.
• Estrogen: The major reproductive hormone released by growing follicles on the ovaries; causes a mare to show heat.
• Progesterone: The major reproductive hormone produced by the corpus luteum, a structure that forms on the ovary where an ovulation occurred; it causes a mare to go out of heat.