Developmental competence of goat oocytes from follicles of different size categories following maturation, fertilization and culture in vitro.

The aim of the present study was to investigate the effect of size of from which goat oocytes originate on their subsequent ability to be fertilized and to undergo early embryonic development in vitro. Nonatretic follicles larger than 2 mm in diameter were dissected and distributed into three groups according to size (small: 2-3 mm; medium: 3.1-5 mm; large: > 5 mm). Cumulus-oocyte complexes were isolated from the follicles and only those with a compact multilayered cumulus were selected for in vitro maturation. After maturation, 70%, 83% and 97% of oocytes from small, medium and large follicles, respectively, were at metaphase II. After in vitro fertilization, no significant difference was observed in the cleavage rate 40 h after insemination between oocytes from small (46%) and medium (55%) follicles, and between oocytes from large follicles (69%) and ovulated oocytes (75%). After in vitro culture, significantly more embryos from small follicles arrested before or at the 8-16 cell stage (84% compared with 53%, 45% and 39% of embryos from medium and large follicles and ovulated oocytes, respectively). The proportion of morulae and blastocysts obtained was 10% and 6% from small follicles, 35% and 12% from medium follicles, 29% and 26% from large follicles and 20% and 41% from ovulated oocytes. Oocytes from small and medium follicles yielded a significantly lower proportion of hatched blastocysts (0% and 3%, respectively) than did those from large follicles and from ovulated oocytes (15% and 34%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)