There are few studies about transvaginal ultrasound-guided follicle aspiration in equine medicine regarding potential complications to future fertility of aspirated mares. In order to evaluate the effect of follicular aspiration on subsequent fertility in mares, two experiments were conducted. In Experiment I, fifteen Criollo mares were allocated to one of three groups according to the diameter of the aspirated follicle during estrus: 25-29mm (n=4; Group 1); 30-34mm (n=6; Group 2); > 35mm (n=5; Group 3) and control group (n=15; Group 4). In Experiment II, the follicular aspiration was attempted in twenty-five mares during diestrous, when at least four follicles (> 5mm) were seen in the transrectal ultrasonography of both ovaries. All visible follicles, between 4 and 8 mm, were aspirated. Thirty-one mares served as control. In Experiments I and II, the pregnancy rates in the following cycle after aspiration were 75.0% (Group 1), 83.3% (Group 2), 60.0% (Group 3), and 73.3% (Group 4 - Control); and 76.0% in the aspirated diestrous group and 77.4% in the control group (non aspirated), respectively. On both experiments, pregnancy rates were similar (P>0.05) in treated and control mares. The results of this study show that the conception rates of the first estrus period following follicular aspiration are not affected by the procedure.
equine; fertility; follicular aspiration; mares