Effect of repeated transvaginal ultrasound-guided follicle aspiration on fertility in mares

Abstract Objective—To determine whether performance of transvaginal ultrasound-guided follicle aspiration (TVUFA) repeatedly in mares adversely affects their fertility. Design—Historical prospective study. Animals—23 mares that had never undergone TVUFA and 59 mares that had undergone TVUFA on 1 to 11 occasions. Procedure—Mares were classified into 4 groups according to the number of TVUFA procedures previously performed on the ovary in which ovulation occurred at the time of insemination as follows: group 1, 0 TVUFAs (control group, n = 23 mares); group 2, 1 or 2 TVUFAs (40 mare-cycles); group 3, 3 or 4 TVUFAs (21 mare-cycles); and group 4, 5 to 11 TVUFAs (13 mare-cycles). Each ovary and its associated number of TVUFAs were considered separately; therefore, some of the mares that underwent TVUFA were represented in > 1 group (1 mare was included in group 2 twice [once for each ovary]), and the sample size in groups 2, 3, and 4 was denoted as mare-cycles. Fertility was assessed as pregnancy rates in cycles in which mares were inseminated with fresh or cooled semen from 1 fertile stallion. Results—There were no significant differences in pregnancy rates among groups 1, 2, 3, and 4 (83%, 90%, 81%, and 85%, respectively). Conclusions and Clinical Relevance—Results indicated that repeated performance of TVUFA (as many as 11 times) had no detectable adverse effect on fertility in mares. This finding is clinically important for situations when TVUFA is performed on fertile mares, whether for oocyte collection or other purposes.