Influence of maturation culture period on the development of canine oocytes after in vitro maturation and fertilization.

The objective of this study was to determine an optimum maturation period of canine oocytes for the development in vitro after in vitro fertilization (IVF). Canine oocytes larger than 110 micrometers in diameter, which were collected from ovaries at the follicular phase of the reproductive cycle, were cultured for each time (48, 72 and 96 h) in TCM 199 medium supplemented with 10% canine serum, fertilized, and then cultured in vitro for 8 days. Significantly more oocytes reached metaphase II (MII) in the 72-h culture group than in the 48-h culture group (25.6% vs. 41.0%). The percentages of oocytes that reached MII or beyond after maturation culture did not differ significantly between the 72- and 96-h culture groups, but the percentage of parthenogenetically activated oocytes in the 96-h culture group was significantly higher than that in the 72-h culture group. The percentages of cleaved embryos after IVF were significantly higher in the 48- and 72-h culture groups than in the 96-h culture group. In the 48-h culture group, 3.9% of fertilized oocytes developed to the 16-cell stage or beyond, but none of the cleaved embryos in the 72- and 96-h culture groups developed to the same stage. These results indicate that full nuclear maturation of oocytes collected from ovaries at the follicular phase occurs after 72 h of in vitro culture. However, an optimum maturation period (48 h) for the in vitro development of canine oocytes after IVF may be different from the period necessary to reach the maximal oocyte maturation rate, when based on the developmental stage of the cleaved embryos.