Published February, 2015

Barry Ball, DVM, PhD, Dipl. ACT, the Albert G. Clay endowed chair in equine reproduction and a professor in the department of veterinary science at the Gluck Equine Research Center, spoke about reproduction in the geriatric mare during the 6th Annual Kentucky Breeders’ Short Course.

Older mares experience several uterine changes. Ball focused on pregnancy and ovarian, oviductal, and uterine factors. Unlike humans, mares do not undergo menopause, although their eggs do deplete eventually. Ball emphasized that a mare’s actual age and reproductive age are not the same. The reproductive age is dependent on the number of oocytes (eggs) populated in the mare’s ovary at birth.

Therefore, fertility decreases as the antral follicle count, or ovarian reserve, diminishes. Ovarian senescence refers to an ovary with no antral follicles or a depleted ovarian reserve. Ball said there will eventually be a marker to determine older mares’ reproductive age. This would allow individuals to predict how fast a mare will age reproductively.

Anovulatory hemorrhagic follicles (AHF) are follicles that do not ovulate but fill with a blood clot. AHF incidence is directly correlated to increasing age in mares and is also associated with a prolonged estrous cycle, or days between ovulation, if a mare is bred but does not ovulate. This causes low fertility

In the oviduct, the geriatric mare has a higher risk for oviductal plugs. W.R. Twink Allen, BVSc, PhD, ScD, DESM, MRCVS, director at the Paul Mellon Laboratory of Equine Reproduction, in  the United Kingdom, developed technology using a hormone called prostaglandin E (PGE2) to manage these mares. Using PGE2 as a topical treatment for relaxing the oviduct’s smooth muscle looks to be a possible solution for releasing these plugs from the oviduct, Ball said.

The geriatric mare has an increased risk of uterine problems such as endometritis (inflammation of the uterine
lining), endometrial cysts (fluid-filled structures in the uterine lining), and endometriosis (when the uterine lining
grows outside the uterus).

A mare older than 10 years who has not previously given birth might have issues with cervical changes and adhesions, which can cause fluid accumulation in the uterus and delayed uterine clearance of fluid. Endometritis can result in early embryonic loss. Fertility declines when mares are between the ages of 10 and 13. As age increases, the rate of embryonic loss continues to increase as well. Other pregnancy problems include retarded fetal growth, placental insufficiency, uterine artery rupture, and prepubic tendon rupture.

Ball concluded by restating that older mares experience a reduced oocyte reserve and increased early pregnancy
loss. They are also more susceptible to uterine diseases such as endometriosis, angiosis, lymphatic cysts, and placental insufficiency.

Hannah Forte is a communication intern with the UK Ag Equine Programs and Gluck Equine Research Center and undergraduate student majoring in community and leadership development at UK.