Follicular correlates with in-vitro fertilization in cattle

The follicular microenvironment may affect the quality and the fertilizability of an oocyte in vivo as well as in vitro. Determination of the concentrations of certain follicular fluid compounds upon aspiration could therefore be used as important clinical measures to predict the developmental ability of an oocyte submitted to in-vitro fertilization. In cattle gonadotrophin stimulation (superovulation) frequently leads to perturbed follicular steroidogenesis and oocyte maturation, and fertilization rates in vivo as well as in vitro may be reduced. These abnormal changes are monitored in the peripheral profiles of LH, progesterone and oestradiol-17 beta during the periovulatory period, and measurements of these hormones may be used to discriminate between good and poor oocyte donors. Concurrent measurements of progesterone and oestradiol-17 beta in the aspirated follicular fluids and determination of the cytogenetic features of the oocytes will reflect these deviations but, because the variation between follicles within an animal is so large, it is not possible to rely on single hormone determinations; if attempted they should be interpreted with caution. Presently, no non-invasive method such as steroid measurement and flow cytometry accurately reflects oocyte quality and function in cattle and it is seriously questioned whether such clinically applicable methods are valid. It is suggested that evaluation of oocyte quality is done on three levels: (1) the animal (peripheral hormones), (2) the ovary (stimulation, premature ovulation, follicular appearance); and (3) the follicle (cumulus oophorus complex, steroids).