Breeding the Older Mare, PT 2

Welcome back folks to the discussion we began here at My Stable Life regarding the breeding of older mares. Yesterday in Breeding the Older Mare, PT 1, we talked a bit about the importance of uterine health and how things change over time, in the aging mare. Today, let\’s examine a few of the other challenges that can plague the older broodmare.


Contamination and/or infection during breeding can cause unsuccessful breedings in all ages of mares because inflammation in the uterus can destroy the semen or the embryo. Endometritis occurs when there is inflammation of the uterine lining. All mares experience some degree of inflammation after being bred (in response to semen, which is a foreign substance to the uterus), but most mares clear this inflammation within 24 hours. Healthy mares can put enough of an immune response forward to deal quickly with inflammation and any bacteria that were introduced with breeding, well ahead of arrival of the fertilized egg traveling down the fallopian tube. But in some mares, especially older mares, inflammation, uterine fluid, or infection remains, so the embryo does not survive and the mare comes back into heat.

In older mares, contamination or infection is also commonly caused due to poor anatomical conformation which in turn causes the reduced efficiency of the anatomical barriers that help keep infection and urinary, fecal, and air-born contaminants out of the reproductive tract.

Past foaling traumas or Caslick\’s operations can cause the vulva to tilt and sink inwards, allowing urine or feces to pool in the area and contaminate her reproductive tract. Or it may be as simple as the lips of the vulva not sealing properly. Additionally, the vestibulovaginal fold, a fold of tissue about a third of the way between the lips of the vulva and the cervix can become nonfunctional due to anatomical changes. And lastly, mares who have experienced trauma to the cervix from difficult foalings in the past may not be able to form a tight cervical seal any longer to prevent bacterial infections.

Numerous foalings can also be problematic in that it results in the stretching of support ligaments for the uterus and repeated damage to innervation of the uterus. That in turn, contributes to poorer uterine clearance because innervation is what causes the muscles to contract.

Conversely, not foaling enough can also be a problem. Many people believe that a mare who is not in foal every year, can affect her fertility. If the mare goes through multiple heat cycles, sometimes the wear and tear to her uterus becomes more severe as opposed to keeping her pregnant. Every time a mare comes into heat and the cervix relaxes, a little bit of contaminant goes into the uterus from the vagina. A pregnant mare doesn’t have these multiple cycles, so you don’t have that little bit of wear and tear occurring during each one of those reproductive cycles.

That\’s it for today. MSL will be back next week with more on the topic of breeding older mares. Until then, stay warm!


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