If one were to ask your veterinarian what type of mare he or she thought was the toughest to get bred and have carry to term, don't be surprised if they come back with the answer, the teenage maiden mare. One would think naturally the opposite.

Although an older maiden mare has never been bred before, they are susceptible to post breeding endometritis. Many times, mares that have had a show jumping or dressage career may not be presented to be bred until they are in their teens, and as said before they can be very difficult to get in foal. They tend to fit into a syndrome  where if one examines their uterine biopsies, these samples routinely reveal glandular degenerative changes and fibrosis. These changes will limit their ability to resist bacterial infections, and will also influence in a negative capacity the ability of the uterus itself to support the pregnancy hormonally (progesterone levels will be subnormal).

Another common characteristic of these mares will be there inability to eliminate uterine fluid.  An older maiden mare often has an abnormally tight cervix that fails to relax properly during estrus: as a result, fluid is unable to drain properly, and it accumulates over time inside the interior space. In many cases the fluid itself is devoid of bacteria and there may be no evidence of inflammatory cells either. This brings out the necessity for a good, sound, and thorough diagnostic evaluation of her uterine environment. This is accomplished with the use of ultrasound, which will provide a specific, valuable interpretative view of her uterine. In conjunction with this procedure it is very important to perform a uterine culture (to rule out the presence of bacteria), and a uterine cytology (to rule out the presence of inflammatory cells).  These procedures will let us understand the origin and significance of the uterine fluid present, and how best to help eliminate it.

After the mare is bred, the fluid accumulation will be aggravated due to poor uterine muscular contractions and the presence of a tight cervix. It has been recently discovered that these mares have vascular (blood vessel) degeneration that will compound their inability to clear their uterus of fluid and bacteria. For this reason alone, it is highly recommended that the veterinarian in charge consider the benefit of a uterine biopsy prior to breeding. This will allow the owner a specific insight into the ability of their mare to become pregnant in the first place and what are the percentage chances that she will carry to term successfully.

Contributed by John Fling, DVM


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