THE EFFECTS OF EXOGENOUS GONADOTROPINS ON OOCYTE AND EMBRYO QUALITY IN CATTLE

It is well documented and unfortunately accepted that approximately 15 to 20% of all donor cattle superstimulated with eCG or FSH yield no transferable embryos. In the present paper, some factors leading to reduced oocyte and embryo quality are discussed. We have focused firstly on certain endocrine and oocyte maturational features which take place during the period of luteal regression, i.e. the period from PGF2 alpha administration until the preovulatory LH surge, and secondly, on the relationship between the superovulatory response and the embryo quality on Day 7. We conclude that: 1) treatment with eCG or FSH causes increased estradiol-17 beta plasma levels, suppressed episodic LH secretion, earlier occurrence of the LH surge and the nucleoli of oocytes from undergoing the normal vacuolization in a certain proportion of donor cattle, 2) although subtle and hardly measurable, these deviations have a profound effect on the subsequent embryonic developmental capacity, 3) the superovulatory response does not affect the subsequent viability of embryos transferred on Day 7 and 4) optimization of the donor's reproductive physiology is the only way to reduce the incidence of non-transferable embryos.