Inability to Impregnate a Mare
History. A 14-year-old American Saddle-bred mare has been bred two times this season and still is not pregnant. The mare has had three prior foals without any difficulty. This season the owners have had the mare bred by artificial insemination (AI) at the barn where the stallion is kept.
The trainer wanted more control over the situation, and she is now going to have the mare kept here. The semen will be shipped here for Al breeding. The trainer has had the semen measured to ensure that the motility is good, which it is. The mare has had a uterine culture and cytology performed, which are within normal limits. On previous ultrasound examinations the marc had no fluid in her uterus and no other abnormalities (e.g., cysts). The stallion is only collected on certain days of the week, so the mares cycle must be timed so that the semen will arrive before the mare ovulates.Clinical Examination. The mare is in good body condition. Based on her previous history and diagnostics, it appears that she has a cycle that is difficult to follow. Most mares will ovulate a follicle that is at least 35 mm. Additional parameters to assess when she will ovulate include the following: her cervix will be very relaxed, her edema will maximize and then start to regress, and her progesterone level should be 0 ng∕mL. On palpation, the mare has a large corpus Iuteum (CL) present on one ovary, and she appears to be in diestrus. Because it is desirable to get her back in heat as soon as possible, the mare is given PGF2ir This will cause regression of the CL, and the mare should be in heat in 5 to 7 davs.
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Comment. It is not clear why the mare has not yet become pregnant. The semen appears to be of good quality, and the mare does not appear to have any preexisting conditions that decrease her fertility. The mare will be followed closely to optimize her potential for a pregnancy.
Treatment. The mare is rechecked 4 days after the administration of PGF2α. She has a 3()-mm follicle on the right, multiple small follicles (MSFs) on the left, but no edema, and the cervix is toned. The mare is rechecked 2 days later, and she has a 35-mm follicle on the right, a 25-mm follicle on the left, edema is 2 (of 3), and cervix is starting to relax. To be sure that she is not missed, progesterone is checked and is I to 2.5 ng∕mL. She will be ready to breed soon. The stallion trainer is called because it is anticipated that semen will be needed the following day. The recheck of the mare on the next day shows a 38-mm follicle on the right, MSFs on the left, and edema of 3, with a relaxing cervix (2). Semen is ordered for the next day. The next morning the mare has greater than a 40-mm follicle on the right, MSFs on the left, 3+ edema, and cervix is a 3. Her progesterone is 0 ng∕mL. When the semen arrives, the motility, morphology, and numbers are good, and the mare is bred. She has a 42-mm follicle on the right, MSFs on the left, edema of 3, and cervix is a 3. Although it is anticipated, based on her cycle, that she will ovulate that night, she is given one dose of human chorionic gonadotropin (hCG). This will stimulate FSH and LH to help induce ovulation. When the mare is checked the next morning, she has ovulated. The mare is checked again at 14 days and found to be pregnant. She is rechecked at 24 days, and she is still pregnant. The fetus is growing, and a fetal heartbeat is detected.