Fertile Conformation in Horse Breeding

Breeding your mare will be much easier if she is built for the job.

From The American Quarter Horse Journal

A good reproductive conformation is important for broodmares. We’ll tell you what that consists of. Journal photo.

Dr. Michelle LeBlanc has spent more than 25 years working on the mare side of equine reproduction. She knows that a mare’s external form counts when you’re assessing her ability to function as a broodmare.

Reproductive Conformation

  • The first thing Dr. LeBlanc looks at is the perineal conformation.
  • The “perineum” is the group of muscles located between the anus and the vulva.
  • Look at the vulva and the anus; they should be vertical with no tilt.
  • If there’s a tilt, the rectum often looks sunken in and the vulva slants toward the mare’s head.
  • It’s not uncommon for mares with a tilt to their perineal conformation to contaminate the vagina with fecal material.

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Another thing to look at is where the vulva sits in relation to the pelvis.

“There are some mares that may aspirate small amounts of fecal material into their vulva because there’s a large amount of the vulva that is open above the brim of the pelvis, even though they’re not tilted,” Dr. LeBlanc explains.

A mare with a tilt to her perineum or with too much of the vulva above the pelvic rim may require a Caslick’s procedure to prevent contamination. The veterinarian sutures shut the lips of the vulva down to the brim of the mare’s pelvis.

A mare with poor reproductive conformation can have:

  • Vaginal contamination from air or feces
  • Uterine infection/inflammation
  • Urine pooling
  • Difficulty foaling (resulting in rectal tears, etc.)

“If I have a mare that’s constantly dealing with infection and fluid in her uterus, the first thing I check is whether or not she needs a Caslick’s, based on her conformation,” says Dr. LeBlanc.

Causes of Poor Reproductive Conformation

Many factors can cause poor reproductive conformation. Perhaps the most common relate to physical changes in the mare that occur over time, due to aging and/or the number and size of a mare’s foals.

Physical Changes Over Time

  • With age, and after carrying several foals, the broad ligaments that maintain stability in the uterus stretch, dropping the uterus further down into the abdomen.
  • If a mare has a large foal, then the uterus drops lower and eventually does not snap back, especially if the mare has had a lot of big and heavy foals.

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  • Foaling Injuries Can Be Caused By:
  • Very large foals
  • Pulling too soon before the mare has had time to relax
  • Failure to open a Caslick’s
  • Rips in a mare with a small vulva

Poor Body Condition

Simply being underweight can cause a mare’s perineum to tilt.

  • Fat is necessary to maintain the proper relationship between the vulva and the pelvis.
  • If a mare gets too thin, the lack of fat can cause the vulva and pelvis to shift out of position.
  • Good body condition in broodmares is very important.


“The other cause is that they’re just built that way,” Dr. LeBlanc says.