The Chronically Infertile Mare

Infertility or more appropriately, subfertility is frustrating to manage because many factors impact fertility. Seasonality, aging, systemic problems such as laminitis or Cushing’s disease, nutrition, obesity, group dynamics, and environmental conditions such as temperature or rainfall can all interfere with reproduction. In addition, the estrous cycle changes dynamically from the transitional phase in the spring to recurring estrous cycles and from estrus itself to diestrus or pregnancy. Hormonal signaling must be exquisitely synchronized with physical changes of the reproductive tract and deposition of fertile semen in the uterus for pregnancy to occur. Asynchrony of these events, infection, inflammation, previous trauma to the reproductive tract, or “stress” can interfere with conception and maintenance of pregnancy. Most cases can be solved with a methodical, thorough physical and reproductive examination and appropriate diagnostic laboratory aids; however, there certainly are infertility cases that reproductive specialists would rather not see walk into the clinic. Repeated examinations may be required to identify subtle abnormalities that may occur only during certain stages of the estrous cycle. Treatment protocols should be designed around the diagnosis, and antibiotics, ecbolics, or steroids should not be used indiscriminately. The causes of chronic infertility are many (Table 1), but clients present mares for only a few reasons or “complaints.” Because most of us deal with “complaints,” the causes for infertility are organized under four common client complaints. They are (1) mare exhibits abnormal or no estrous cycles, (2) mare accumulates fluid in her uterus during or immediately after estrus, (3) mare has repeated uterine infections, and (4) mare looses the pregnancy after the 14-day examination. It is assumed that the mare was bred by a fertile stallion and that the dose of cooled or frozen semen used for insemination was adequate. However, this should never be taken for granted when evaluating a mare for infertility, because a subfertile stallion bred to a subfertile mare greatly decreases the likelihood of pregnancy.