Repeated Follicle Aspiration Doesn't Affect Fertility

Veterinarians are increasingly using repeated transvaginal ultrasound-guided follicle aspiration (TVUFA) to collect eggs from mares for research and clinical applications. Currently, the main use of TVUFA for client-owned mares is for oocyte transfer, which involves collecting an egg from a subfertile mare and transferring it to a fertile recipient mare where it is fertilized.

In contrast to its clinical use, TVUFA is routinely performed on fertile mares for research applications. It's long been known that even though the procedure is minimally invasive, multiple follicle aspirations can cause fibrosis in the mare's ovarian stroma (the supporting tissue of the ovary), but researchers were unclear if this would actually affect the mare's fertility.

Researchers at the University of Idaho examined 23 mares that had never undergone TVUFA and 59 mares that had undergone TVUFA at least once, but not more than 11 times. The researchers' objective in this study was to see if repeatedly performed TVUFA in fertile mares would adversely affect their fertility.

Study horses were separated into four groups: Group 1 (the control) included 23 mares that had not undergone the procedure, Group 2 included mares with one or two TVUFAs, Group 3 included mares with three or four TVUFAs, and Group 4 included mares with five to 11 TVUFAs.

According to Dirk Vanderwall, DVM, PhD, Dipl. ACT, of the department of animal and veterinary science at the University of Idaho, the study showed that the average pregnancy rate for mares in Group 1 was 83%, in Group 2 it was 90%, in Group 3 it was 81%, and in Group 4 it was 85%. The researchers concluded, "There were no differences in pregnancy rates between control mares that have never undergone TVUFA and mares that had undergone TVUFA previously."

Vanderwall explained the potential for the study's results were twofold. "We were routinely performing transvaginal ultrasound-guided follicle aspiration on our research mares for our cloning work, and we wanted to know: Could we potentially be altering the fertility of our mares?" Vanderwall said. "We were very encouraged by the results of the study.

"For the horse owner, the study has relevance for the potential application of the new intracytoplasmic sperm injection (ICSI) procedure," he added.

During ICSI, a single sperm can be injected into the mare's egg. The procedure is used to produce foals from stallions with poor-quality or limited sperm. "If the horse owner had a fertile mare from which they wanted to collect oocytes (eggs) to use for the ICSI procedure, there would be no adverse effects on the fertile mare's subsequent fertility," Vanderwall said.

Researchers included in this study published in the Jan. 15 issue of the Journal of the American Veterinary Medical Association were Vanderwall; Kevin Hyde, DVM; and Gordon Woods, DVM, PhD, Dipl. ACT.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for .

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