Once the mare is at the clinic, a transrectal ultrasound exam will initially be performed to confirm pregnancy status (pregnant or open), determine the presence or absence of a corpus luteum, assess the diameter of the largest follicle(s) on each ovary, and evaluate the uterus for the presence of edema and/or free fluid in the uterine lumen. Ultimately, the goal of the first exam is to determine if the mare is cycling, determine the stage of the estrous cycle (estrus or diestrus), and identify any ovarian or uterine abnormalities.
As a side note, we have had mares arrive at the clinic for breeding management that are already pregnant, unbeknownst to the owner. Consequently, pregnancy status verification is a critical early step in the initial evaluation process.
If the mare has minimal follicular development and appears to still be in seasonal anestrus (i.e. not cycling yet), it may be recommended that the mare return home and come back for a re-check examination in 7 to 14 days. If a mare was schedule to be transported to the Equine Reproduction Laboratory from a long distance, it is advantageous to have a local veterinarian perform an ultrasound examination before shipping the mare and consider sending the mare once it is confirmed that the mare is cycling. This would avoid a potentially prolonged period waiting for the mare to begin normal estrous cycles.
If the mare has a history of subfertility, pregnancy loss, or if the initial examination reveals the presence of fluid in the uterine lumen, it will be recommended that a uterine culture and cytology be performed to determine if the mare has a bacterial infection in her uterus. Results of the culture and cytology are generally available within 24 to 48 hours after sample collection.
If the initial examination reveals that the mare is cycling and has a corpus luteum present on one ovary, it may be recommended to administer a dose of prostaglandins to lyse (regress) the corpus luteum and allow the mare an earlier opportunity to come back into heat. The general term for this common hormone therapy procedure is “short-cycling” the mare. Most mares will come into heat within 3 to 4 days and may be bred within 5 to 9 days after prostaglandin administration.
Reproductive management for breeding with fresh semen (stallion on site)
An ultrasound examination will be performed as the mare comes into estrus (heat). Additional exams will be performed periodically to monitor follicle development. Once a follicle ≥ 35 mm in diameter is identified and there is a normal degree of uterine edema present, the stallion selected by the mare owner will be collected, the semen evaluated and one or more breeding doses prepared.
The mare will be inseminated with a dose of the freshly collected semen and the mare will be administered a dose a hormone to induce ovulation; the hormone will either be a GnRH agonist, such as histrelin or deslorelin, or human chorionic gonadotropin.
An ultrasound examination will be performed the following morning to determine if the mare has ovulated and monitor for uterine issues. If a second breeding dose is available and the mare does not have any uterine issues, the mare may be re-inseminated the following morning.
Ultrasound examination will be performed as needed to confirm the day of ovulation, which is anticipated to occur 36 to 40 hours after administration of the ovulation induction agent.
If the mare is being bred to carry her own pregnancy, an ultrasound examination will be performed 14 days post-ovulation to confirm pregnancy status.
Reproductive management for breeding with cooled-transported semen (stallion not on site)
Management procedures are increased for mares being bred with cooled-transported semen. It is critical to know in advance the semen collection schedule for the stallion and the semen shipment options, such as overnight courier (FedEx, UPS, etc.) or counter-to-counter airline shipment.
Once the mare comes into estrus and develops a follicle ≥ 30 mm in diameter is identified and there is a normal degree of uterine edema present, the stallion owner or manager will be contacted to arrange for semen collection and shipment (‘pencil-in’ for semen collection).
Early in the morning on the collection day, the mare is examined again by ultrasound to confirm follicle status. The stallion owner or manager is contacted again to confirm the semen order.
Once it has been confirmed that 1) the mare is on the collection list, 2) the stallion has been collected and 3) one or more doses of semen have been shipped, the mare is administered an ovulation induction agent. A conservative alternative is to administer the agent once the semen has arrived safely and the mare has been inseminated.
It is important to evaluate the semen on arrival and prior to insemination. The semen dose should be removed from the shipping container, gently mixed and a small aliquot of semen removed for evaluation. A drop of semen may be placed on a slide for immediate evaluation for motility, but it is important that the small aliquot be warmed to 37° C over a 10-minute period before evaluation for total and progressive sperm motility. The motility parameters are recorded into the reproductive record of the mare.
As noted previously, the mare will subsequently be monitored for ovulation and uterine issues, such as persistent breeding-induced endometritis. Reproductive management for breeding with cooled-transported semen (stallion not on site).
Management procedures are increased for mares being bred with cooled-transported semen. It is critical to know in advance the semen collection schedule for the stallion and the semen shipment options, such as overnight courier (FedEx, UPS, etc.) or counter-to-counter airline shipment.
Once the mare comes into estrus and develops a follicle ≥ 30 mm in diameter is identified and there is a normal degree of uterine edema present, the stallion owner or manager will be contacted to arrange for semen collection and shipment (‘pencil-in’ for semen collection).
Early in the morning on the collection day, the mare is examined again by ultrasound to confirm follicle status. The stallion owner or manager is contacted again to confirm the semen order.
Once it has been confirmed that 1) the mare is on the collection list, 2) the stallion has been collected and 3) one or more doses of semen have been shipped, the mare is administered an ovulation induction agent. A conservative alternative is to administer the agent once the semen has arrived safely and the mare has been inseminated.
It is important to evaluate the semen on arrival and prior to insemination. The semen dose should be removed from the shipping container, gently mixed and a small aliquot of semen removed for evaluation. A drop of semen may be placed on a slide for immediate evaluation for motility, but it is important that the small aliquot be warmed to 37° C over a 10-minute period before evaluation for total and progressive sperm motility. The motility parameters are recorded into the reproductive record of the mare.
As noted previously, the mare will subsequently be monitored for ovulation and uterine issues, such as persistent breeding-induced endometritis.
Reproductive management for breeding with frozen semen
Management procedures are enhanced even more for mares being bred with frozen semen. Ideally, one or more doses of frozen semen should be requested prior to the start of the breeding season or prior to arrival of the mare at the breeding center.
Once the mare comes into estrus and develops a follicle ≥ 35 mm in diameter is identified (i.e. Quarter Horse mare; may vary by breed and individual mare) and there is a normal degree of uterine edema present, the mare will be administered a dose of histrelin or deslorelin (ovulation induction agents) at 8 p.m. with the anticipation that ovulation will occur approximately 40 hours later, or approximately 12 p.m. (noon) two calendar days later.
Ultrasound examinations will be performed every 6 to 8 hours from the time of the hormone treatment until ovulation is detected.
If two doses of frozen semen are available for the estrous cycle, one dose would be thawed and inseminate (using a deep-horn procedure) a few hours prior to the anticipated ovulation and the second dose thawed and inseminated immediately after ovulation is detected.
If only one dose of frozen semen is available, the dose would be thawed and inseminated immediately after ovulation is detected.
It is important to examine the mare the day after ovulation to monitor for persistent breeding-induced endometritis.