Breeding Older Mares, PT 1


As discussed yesterday on My Stable Life, there are many things to take into consideration when breeding older mares. How difficult will it be for her to carry a foal to full term this time? Will she need hormone therapy and will the costs of that outweigh other options for breeding her? What is her breeding history? Has she had a foal every year since she was retired to the broodmare band? Etc.

If you have a great mare who you would like to get another foal from but she getting up there in age, the good news is you still have options for breeding. Embryo transfer makes it possible to obtain foals from our great mares, years after their best reproduction days have passed. But regardless of how you choose to proceed, here are some of the reasons breeding your older mare needs extra consideration:



Uterine cysts can sometimes pose a problem for breeding as they are usually seen in conjunction with an increase in the intercellular fluid, the formation of small \”lakes\” within the tissue and early embryonic death. Sometimes cysts can even be mistaken for a small fetus during rectal ultrasounds/palpation. Older mares with a history of multiple pregnancies and births often develop scar tissue within the uterus. The scar tissue can cause a clogging of channels in the lymphatic drainage system which means there is literally a backup of fluid at these locations. The fluid is then secreted by glands within the uterus with the correct levels being maintained via drainage through the uterine walls. Problems can arise when uterine scar tissue clogs portions of this drainage field, resulting in a cyst or cysts filled with fluid.

Depending on your veterinarian, 2 or 3 cysts may not concern them unless a cyst has become so large that it fills the lumen of one horn or the other. If this happens, embryo migration throughout the uterus could be impeded resulting in lack of maternal recognition of pregnancy.

If the mare has multiple cysts, it may still be worth a breeding attempt as you can never know if the cysts will pose a problem for pregnancy until you try. But use common sense and if she does not catch within a couple of attempts, stop trying to breed her. The presence of multiple small uterine cysts are sometimes associated with mucometra, a condition that is characterized by a spongy, thick uterine wall, a flaccid uterus and the presence of milky-white mucus within the uterine cavity.

If your mare has cysts, it\’s important to document them and their location in her reproductive system, in the event you want to continue breeding her in future years. The information is helpful for your reproductive specialist.

Fibrosis is another of the degenerative changes often seen in an older mare\’s uterus, and it is mainly due to aging rather than to wear and tear from pregnancies. Fibrosis is defined as an abnormal increase in the amount of fibrous connective tissue in an organ, part or tissue.

Statistically, pregnancy loss is higher in older mares than it is  in younger horses. Some research has shown that the villi in the uterus are less numerous in some older mares as a result of fibrosis. Thus the placental area (for attachment) is greatly reduced. And when this happens, a fetus may not be as well-nourished as it should be. Despite your best efforts, the resulting foal is small and weak and you won\’t even know it until it\’s born.

Tomorrow, we\’ll talk about infertility of the older mare, endometritis, repeated foaling and not foaling enough. See ya then!


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