Changes in the cumulus-oocyte complex of subordinate follicles relative tofollicular wave status in cattle

Citation
Df. Salamone et al., Changes in the cumulus-oocyte complex of subordinate follicles relative tofollicular wave status in cattle, THERIOGENOL, 52(4), 1999, pp. 549-561
Citations number
51
Categorie Soggetti
Veterinary Medicine/Animal Health","da verificare
Journal title
THERIOGENOLOGY
ISSN journal
0093691X → ACNP
Volume
52
Issue
4
Year of publication
1999
Pages
549 - 561
Database
ISI
SICI code
0093-691X(199909)52:4<549:CITCCO>2.0.ZU;2-1
Abstract
We investigated factors that affect cumulus-oocyte complex (COC) morphology and oocyte developmental competence in subordinate follicles on different days after follicular wave emergence in beef heifers. In Experiment 1, heif ers (n = 13) were assigned at random to COC aspiration during the growing/s tatic (Days 1 to 3) or regressing (Day 5) phase of subordinate follicle dev elopment (follicular wave emergence = Day 0). Follicular wave emergence was induced by transvaginal ultrasound-guided follicular ablation, ovaries wer e collected at slaughter, all follicles greater than or equal to 2 mm excep t the dominant follicle were aspirated, and COC were microscopically evalua ted for morphology. There was a greater percentage of COC with expanded cum ulus layers on Day 5 (42.4%) than on Days 1 to 3 (2.2%). In Experiment 2, h eifers (n = 64) at random stages of the estrous cycle had all follicles gre ater than or equal to 5 mm ablated and 4 d later, 2 doses of PGF were injec ted 12 h apart; heifers were monitored daily by ultrasonography for ovulati on (Day 0 = follicular wave emergence). Heifers were assigned to the follow ing time periods for oocyte collection from subordinate follicles: Days 0 a nd 1 (growing phase), Days 2, 3 and 4 (static phase), and Days 5 and 6 (reg ressing phase). Ovaries were individually collected at slaughter, and all f ollicles greater than or equal to 2 mm except for the dominant follicle wer e aspirated. The COC were morphologically evaluated and then matured, ferti lized and cultured in vitro. Expanded COC were more frequent during the reg ressing phase (53.4%) than the growing or static phase (14.4 and 17.8%, res pectively; P<0.05). While the proportions of COC with greater than or equal to 4 layers of cumulus cells and denuded oocytes were higher (P<0.05) in t he growing and static phases, the production of morulae was highest (P<0.05 ) with COC collected from subordinate follicles during the regressing phase . In Experiment 3, heifers (n = 18) were assigned at random to oocyte colle ction from subordinate follicles 3 and 4 d (static phase) or 5 and 6 d (reg ressing phase) after follicular wave emergence. The heifers were monitored ultrasonically for ovulation (Day 0 = follicular wave emergence); COC were collected from all follicles (greater than or equal to 5 mm) except for the dominant follicle by transvaginal ultrasound-guided follicle aspiration 3 to 6 d later. Recovered oocytes were stained and examined microscopically t o evaluate nuclear maturation. A higher proportion of oocytes collected on Days 5 and 6 showed evidence of nuclear maturation (50%) than on Days 3 and 4 (8.3%; P<0.05). Results support the hypothesis that COC morphology and o ocyte developmental competence change during the growing, static and regres sing phases of subordinate follicle development. (C) 1999 by Elsevier Scien ce Inc.