Q: I have a 21-year-old mare currently being treated for a guttural pouch infection that was diagnosed by endoscope--we're just waiting for cytology results. Earlier in the year she was successfully bred by shipped semen, put on Regumate, but still lost the embryo at around two months. She's previously had four foals.

My veterinarian says the guttural pouch infection could have possibly been the reason for the loss. Can a experienced reproductive specialist please comment?

Suzanne, via e-mail

A: There are numerous causes for pregnancy loss in a mare. I could not determine from your question if the mare was diagnosed with the guttural pouch infection near the time the pregnancy loss was detected. If this is the case, it is possible that there was a hematogenous (through the blood) spread of infection that reached the uterus and resulted in the demise of the pregnancy.

The stress of the illness may also have contributed to the pregnancy loss. In a recent retrospective study we performed, mares that had significant illness during pregnancy had a higher rate of pregnancy loss. This is similar to results obtained by Liz Santschi, DVM, Dipl. ACVS, associate professor at The Ohio State University, when studying hospitalized pregnant mares. One way to determine if this was the cause would have been to perform a uterine culture at the time the pregnancy loss was ¬detected.

Another question this brings up is when was the mare last determined to be pregnant? We know she was not pregnant at 60 days, but when was she last checked? If she was last checked at 15 days for example, she could have lost the pregnancy at 16 days or at 59 days. That is a large window. If she was last checked at 45 days, that window is much smaller.

Early pregnancy loss is generally related to uterine infection or inflammation. If an infection is present, administering progestins (progesterone, Regumate) generally will make the infection worse as the progestins decrease the uterine immune response. Is her cervix intact? How is her perineal conformation? If the external barriers to infection are compromised, there is a greater likelihood of uterine infection/¬inflammation and pregnancy loss.

A genetic defect is another possible cause. Higher on the list would be "old eggs." Twenty-one is old--reproductively speaking--for a mare. As a mare ages, so do her oocytes (eggs). There is a higher incidence of pregnancy loss in older mares as compared to young mares. As you can see, there are a variety of potential causes for pregnancy loss in the mare. The guttural pouch infection may have been the cause, but it could just as easily have been for a multitude of other reasons.

About the Author

Pete Sheerin, DVM, Dipl. ACT

Pete Sheerin, DVM, Dipl. ACT, is a practitioner at the Rood and Riddle Equine Hospital in Lexington, Ky.

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