OOCYTE QUALITY IN SMALL ANTRAL FOLLICLES IN THE PRESENCE OR ABSENCE OF A LARGE DOMINANT FOLLICLE IN CATTLE

The aim of these experiments was to determine whether the presence of a dominant follicle affects the developmental competence of oocytes fr om small antral follicles of cattle. In Expt 1, oocytes or follicular fluid samples were collected from follicles 2-7 mm in diameter before (day 3 of the oestrous cycle; n = 4) or after (days 6 and 7 of the oes trous cycle; n = 6) emergence of the first wave dominant follicle (ver ified by rectal ultrasonography). Five to ten follicles were aspirated for the determination of individual follicular fluid concentrations o f oestradiol, progesterone, testosterone and dimeric inhibin; oocytes from the remaining follicles from each cow were pooled and development al capacity assessed by in vitro fertilization and maturation. In Expt 2, ovaries containing a young corpus luteum and with or without a lar ge oestrogen-active follicle were collected from the abattoir. Follicu lar aspirates from small follicles in each pair of ovaries were pooled , and oocyte quality and steroid concentrations were determined. In Ex pt 1, small follicles obtained before emergence of the dominant follic le contained significantly more oestradiol than they did after emergen ce (19.5 +/- 1.5 versus 0.7 +/- 1.1 ng ml(-1), respectively; P < 0.05) , but there were no significant differences in concentrations of proge sterone, testosterone or dimeric inhibin. The percentage of blastocyst s obtained from oocytes collected before (12.1 +/- 9.0) or after emerg ence (11.8 +/- 7.0) of the dominant follicle did not differ significan tly (P > 0.05). In Expt 2, follicular steroid concentrations did not d iffer in small follicles taken in the presence versus the absence of a large oestrogen-active follicle, and there were no differences in the developmental capacity of the oocytes. There were significant negativ e correlations between follicular oestradiol concentration and the per centage of blastocysts formed from two-cell (r = -0.90; P < 0.01) and eight-cell embryos (r = -0.65; P < 0.05). These data suggest that in c attle the developmental competence of oocytes from small antral follic les is not adversely affected by the presence of a dominant follicle.