| Summary: | he IVM of canine oocytes is characterized by low rates of metaphase H. The objective of this study was to evaluate the effects of hCG on mciotic development of canine oocytes for culture periods up to 96 h. Oocytes were collected after ovariohysterectomy. Only oocytes > 110 mu m in diameter, with a homogeneous dark cytoplasm and three or more layers of compact cumulus cells were used. For IVM, the COCs were cultured in TCM-199 + 10% fetal calf serum, without (medium A control) or supplement with 10 IU/mL of hCG (medium B), or with a combination of both media (treatment B/ A). The COCs were randomly allocated into three groups. The first and second groups were cultured in either medium A or B, respectively for 24, 48, 72, and 96 h. Oocytes of the third group (treatment B/A) were incubated in medium with hCG (medium B) the first 48 h and then transferred to medium without hCG (medium A) for an additional 24 or 48 It. The proportion of COCs with cumulus cell expansion was also evaluated before fixation. Oocytes were stained with propidium iodide prior to nuclear assessment (with epifluorescence microscopy). COCs with cumulus expansion were evident after 48 h of culture. The proportion of COCs with cumulus expansion was higher (P < 0.05) for media containing hCG (B or B/A) than for meda lacking hCG (A); this difference was maintained for and 96 h in culture. In media A. B and B/A. 23.3, 31.7 and 29,51/(, respectively. ofoocytes were at metaphase II after 72 h, with 20.7. 33.1 and 43.4% at this stage after 90 h. The advancement of meiosis was directly proportional to the time of incubation the highest percentage (P < 0.05) of oocytes at rnetaphase II was observed after 96 h of culture when 10 IU/ml, hCG was present for only the first 48 It of culture.
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