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Dr. McCue Addresses Breeding the Problem Mare

Information from the Pro-ISER (International Symposium on Equine Reproduction) Lecture Series in Equine Reproduction included problem mare breeding from Dr. Patrick McCue.
Dr. Patrick McCue

Dr. Patrick McCue discussed dealing with "problem" mares at the 2020 Pro-ISER (International Symposium on Equine Reproduction) Lecture Series in Equine Reproduction.

When owners have specific goals for their mares and scheduling is tight due to the limited breeding season, being faced with a “problem” mare can be frustrating. Patrick McCue, DVM, PhD, DACT, from Colorado State University, has extensive experience helping owners overcome the obstacles associated with getting these mares in foal.

McCue was able to share his experience and expertise during the first Pro-ISER (International Symposium on Equine Reproduction) Lecture Series in Equine Reproduction held October 23 and 24, 2020. He began his discussion by defining “problem” mares as: 

  1. those not pregnant after being bred to a fertile stallion over three estrous cycles;
  2. can’t carry a foal to term successfully;
  3. have known reproductive pathology; or 
  4. behavior issues related to reproduction.

McCue addressed several of the more common reproductive issues that contribute to a mare being deemed problematic, including the following.

Persistent Mating-Inducted Endometritis (PMIE)

“All mares develop a transient inflammatory response to the presence of the spermatozoa in the uterus. The inflammation peaks about 8-12 hours after mating and should resolve within 24 hours,” McCue said.

Persistent mating-induced endometritis (PMIE), recognized by echogenic fluid in the lumen of the uterus 48 hours after breeding, is one of the most common reproduction issues that McCue sees in clinical practice. PMIE is associated with reduced fertility and tends to be recurrent in affected mares.

“PMIE appears to ‘sensitize’ the uterus, which means that mares with a history of PMIE will often develop the condition at subsequent breedings,” McCue warned.

He added, “Luckily, once we know a mare has a history of PMIE and that she has an increased risk of recurrence, we can anticipate the condition and takes steps to either prevent or reduce the severity of the inflammatory event. Management can then be fairly straight forward.”

Management will probably include the following procedures. 

Timed Ovulation

Veterinarians need to monitor the estrus cycle and initiate a timed ovulation. Breed the mare only once to limit exposure of the uterus to spermatozoa. Then utilize one or more of the following preventative measures:

  • Administer 30-50 mg of dexamethasone IM;
  • Lavage the uterus 4-6 hours post-breeding;
  • Stimulate uterine contractions via administration of oxytocin or a prostaglandin such as Estrumate to help the uterus clear any fluid. A combination of both can be used, but currently McCue said he does not advocate mixing oxytocin and a prostaglandin in the same syringe;
  • Monitor the uterus for the next 2 to 3 days for clearance of uterine fluid;
  • Try to avoid intra-uterine treatments such as uterine lavage or infusing of antibiotics beyond two days post-ovulation.

Watch for Failure of Luteolysis

“Ultrasound examination of a normal mare in diestrus should reveal a corpus luteum on one or occasionally both ovaries, plus an assortment of follicles on each ovary," said McCue. Administration of a dose of prostaglandin to a mare in mid- to late diestrus should result in complete luteolysis."

In some instances, however, an appropriate dose of prostaglandin administered during an appropriate time of diestrus (at least 5 or more days post-ovulation) does not result in complete luteolysis.

“If active luteal tissue is still present after administration of a dose of prostaglandin, the mare will not come into good behavioral estrus and ultrasound examination will reveal an absence of uterine edema, even if there is a growing follicle present,” noted McCue.

The obvious treatment for a mare experiencing incomplete luteolysis is administration of another dose of prostaglandin.

“We do not currently advocate routine administration of multiple doses of prostaglandin or administration of a higher dose of prostaglandin as 90 % or more of mares receiving an appropriate dose of prostaglandin will have complete luteolysis,” advised McCue.

That said, veterinarians should be aware that one dose of prostaglandin is not always sufficient to cause complete luteolysis.

McCue also discussed bacterial endometritis and hemorrhagic anovulatory follicles. More information on these and other conditions can be found in the free 2-volume eBook titled Clinical Equine Reproduction. A free copy can be downloaded here. Currently, the eBooks can only be downloaded onto an Apple device (iPad, Mac laptop, etc.).

The First Pro-ISER webinar, moderated by Dr. Claudia Fernandes from the University of São Paulo, Brazil, served as part of an exciting lead-up to the 13th ISER to be held in 2022. 

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