COMPARATIVE-ANALYSIS OF CALF AND COW OOCYTES DURING IN-VITRO MATURATION

To determine possible causes of reported differences between developme ntal competence of oocytes isolated from prepubertal (10- to 14-week-o ld calves) and adult cows, three parameters were analysed, comparative ly, during in vitro maturation (IVM): (1) oocyte diameter, (2) oocyte energy metabolism, and (3) protein synthesis of oocytes and cumulus ce lls. Cumulus-oocyte complexes were isolated from follicles of 3-5 mm i n diameter in both age groups. Mean oocyte diameter was smaller (P < 0 .02) in calves than in cows (118.04 +/- 1.15 versus 122.83 +/- 0.74 mu m). During the first 3 hr of IVM calf oocytes metabolised glutamine a nd pyruvate at lower rates than adult oocytes, but after 24 hr of cult ure, both molecules were metabolised at the same rate as for adult ooc ytes. A significant decrease in protein synthesis, as measured by [S-3 5]methionine and [S-35]cysteine incorporation was recorded after 9 hr of IVM in calf oocytes, while in adult oocytes a significant decrease in protein synthesis was detected only after 24 hr. After the first 3 hr of maturation, proteins of 130, 26, and 24 kDa were more abundant i n adult than in calf oocytes, while a protein of 55 kDa was more visib le in calf than in adult oocytes. At the same time, among proteins new ly synthesised by cumulus cells, molecules of 405, 146, 101, and 77 kD a were more abundant in adults than in calves. In conclusion, calf ooc ytes and cumulus cells showed several differences when compared with t heir adult counterparts, which are consistent with their reported lowe r developmental competence. (C) 1998 Wiley-Liss, Inc.