Oocyte Yield and the Consequences of Puncture of All Follicles Larger Than 8 Millimeters in Mares

Abstract

Transvaginal ultrasound-guided follicular aspiration was used to study oocyte yield and subsequent ovarian response in mares. In experiment 1, weekly puncture of follicles a 8 mm (an average of 4.3 follicles per mare) produced an average of 0.8 oocytes per mare per week. More follicles were found in saddle mares (5.8) than in pony mares (2.9), and thus saddle mares yielded more oocytes (1.0 vs. 0.6). Compact cumulus surrounded 95% of oocytes recovered from follicles s 20 mm but only 57% of those recovered from follicles > 20 mm. During 11 successive attempts, saddle mares had a linear decrease in the number of follicles. In addition to this general tendency, individual mares showed, from one week to the other, an alternating pattern of either a large follicle (> 20 mm) with several small follicles > 10 mm or no follicle > 20 mm with fewer small follicles. This could be explained by waves of follicular growth. In experiment 2, the puncture in midluteal phase of an average of 5.4 follicles in saddle mares and 3.5 in pony mares produced an average of 1.7 and 1.0 oocytes, respectively. In experiment 3, where successive punctures were performed at 2-5-day intervals, 97% of oocytes obtained at the first puncture had a compact cumulus, but only 74% of those obtained at subsequent punctures did. The percentage of compact cumulus was lower (41% vs. 90%) with a shorter interval (2 days vs. 4-5 days). The suspected cause of this altered morphology was the successive punctures of a follicle, followed by recovery of the oocyte on the second puncture. In experiment 4, the replacement of follicular fluid with PBS, followed 48 h later by oocyte collection, produced oocytes with an expanded cumulus and resumed meiosis, confirming the interpretation of experiment 3.