MORPHOLOGY OF PORCINE CUMULUS-OOCYTE-COMPLEXES DEPENDS ON THE STAGE OF PREOVULATORY MATURATION

The aim of this investigation was to determine the relationship betwee n the morphology of the cumulus-oocyte-complexes (COCs) and the meioti c configuration of oocytes as an LH peak mimicked by hCG. Estrus was s ynchronized in a total of 29 crossbred Landrace gilts by feeding Regum ate(R) for 15 d and administering 1000 IU PMSG. The LH peak was simula ted by treatment with 500 IU hCG at 80 h after PMSG. Endoscopic oocyte recovery was carried out 2 h before and 10, 22 and 34 h after hCG. On ly macroscopically healthy follicles with a diameter of more than 5 mm were punctured. Altogether, 410 follicles from 57 ovaries were punctu red and 251 COCs were aspirated. Oocyte recovery rate increased from 4 8.5 % (P < 0.01) of the early, not yet preovulatory follicles (2 h bef ore hCG) to 80.8 % of late preovulatory follicles (34 h after hCG). Cu mulus morphology in COCs recovered 2 h before and IO h after hCG was h eterogeneous, with most (72.9 to 57.4 %; P<0.01) showing a compact or slightly expanded cumulus. Starting at about 22 h after hCG, COC morph ology changed dramatically (86.7 % of COCs with expanded cumulus; P<0. 01), and 34 h after hCG, 98.3 % of the COCs had only an expanded cumul us. The percentage of oocytes with a mature meiotic configuration incr eased (11.2; 7.1; 41.4 and 70.2 %, respectively, n=238 oocytes; P<0.01 ) as the interval post hCG increased (-2, 10, 22, 34 h, respectively). Meiotic configuration was related to COC morphology: compact COCs -88 .9 % diplotene, expanded COCs - 53.8 % metaphase II (M-II), and denude d oocytes - 69.2 % degenerated chromatin. These results indicate that there is a relationship between oocyte recovery rate, COC morphology, and meiotic configuration and preovulatory follicle maturation after t he application of hCG. (C) 1998 by Elsevier Science Inc.