Factors Affecting the Recovery of Follicular Oocytes and the in vitro Maturation in Horses

Abstract

The aim of this study was to examine the factors affecting the oocyte recovery rates from slaughtered horse ovaries and the maturation rates of the oocytes in vitro. Follicle aspiration provided a constant average of 1.3 oocytes per ovary during winter up to 1.6 oocytes during spring. More oocytes were recovered by additional slicing and washing of the ovaries during winter (3.7) and spring (4.1) than during summer (2.1) and autumn (2.5). The overall recovery rate was 3.6 oocytes per ovary in summer, 4.0 in autumn, 5.1 in winter, and 5.8 in spring. Breed of ovary donors (light and draft horse) was a source of difference in oocyte recovery (4.4 and 7.6 oocytes per ovary, respectively), whereas age of ovary donors did not influence oocyte recovery rates. In vitro maturation rates of compact-cumulus cells-enclosed oocytes in winter (58.3%) and spring (55.5%) were not significantly different, but slightly lower, from those in autumn (65.7%) and summer (64.4%). The maturation rates of oocytes from light and draft horses did not differ (53.7% vs 58.7%, respectively). Storage (3, 6, 9 h) of ovaries in 30°C saline prior to oocyte collection resulted in a maturation rate of 62.3%(3h), 45.0% (6h) and 30.4% (9h), respectively. The number of oocytes per culture drop (50μl volume) had no effect on the maturation rates (1-5; 55.1%, 6-10; 56.3%, 11 -15; 50.8%). Supplementation of the medium with fetal bovine serum or B. S. A. gave similar results as in protein-free culture medium (58.1 %, 62.1 % and 65.3%, respectively). Under different atmosphere conditions (5% CO₂ 95% air; 5 %CO₂ 5 %O₂ 90% N₂), 60, 6% and 53.6% of oocytes reached Metaphase II, respectively.