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Follicular dynamics and superovulation in cattle.

Introduction Over 8000 cows and heifers were superovulated in 1989 in Canada (personal communication, Canadian Holstein Association). The Canadian embryo transfer (ET) industry estimates that nearly 30070 of superovulated cows either fail to respond to a superovulatory treatment (SOV) or only produce a low number of transferable embryos. This constitutes an important economic loss to the ET industry. Approaches to superovulation have remained largely empirical and extreme variability of the superovulatory response is still a characteristic of all of the methods used thus far (1). A great deal of fundamental knowledge of normal folliculogenesis has been obtained over the last ten years and now, rational methods of control of follicular growth during superovulation may be foreseen. Our objective in this paper is to review selected aspects of control of folliculogenesis which set bases for the development of new methods of superovulation.