Relationship between oocyte maturation and fertilization on zygotic diversity in swine

Two experiments were conducted to examine how oocyte maturation and fertilization influence zygotic diversity in swine. In the first experiment, the distribution of oocyte maturation was compared to that of zygotic development. Oocytes were aspirated from follicles of 31 gilts and classified into stages of meiosis. Zygotes were flushed from oviducts of 19 additional gilts and classified into stages of meiosis and fertilization. The second experiment examined whether the time from ovulation to fertilization was constant among all oocytes. To test this premise, four to six oocytes from follicles of 10 mated gilts were aspirated just before or during ovulation, stained and transferred back into the oviducts of these same gilts. Zygotes were recovered 10 h later to determine whether the first oocytes ovulated were the more developed zygotes and, conversely, whether the last oocytes to be ovulated represented the lesser developed contemporaries. The skewed (P less than .05) distribution of oocyte maturation was similar to that of zygotic development. Regression of the frequency distribution describing early oocyte maturation resulted in a line with a slope (.59) that was similar to the slope (.58) of the regressed distribution of zygotic development. Likewise, the order of ovulation and order of subsequent stages of zygotic development were similar. These data suggest that variation in zygotic development in swine was due to variability in oogenesis; the time from ovulation to fertilization appeared to be constant.