The present study was undertaken to establish a relationship between bovine follicle size and oocyte diameter, compare the nuclear maturation competence of oocytes of different diameter groups and the nuclear maturation changes in Korean Native Cattle according to in vitro maturation period.
To compare the relationship between follicle size and oocyte diameter, follicles were dissected, measured, and assigned to one of the following size categories(4≥㎜, 3-4㎜, 2-3㎜, 1-2㎜, and $lt; 1㎜), investigate the maturation competence in the different-sized oocytes, which were divided into three groups( $lt;110㎛, 110 -$lt; 120㎛, and ≥120㎛).
Oocytes were cultured in the culture medium during 0, 6, 12, 18, and 24hrs, respectively, stained, and measured the nuclear maturation degree according to period.
When compared the relationship between follicle size and intrafollicular oocyte diameter, oocyte diameters of three groups of ≥3㎜ follicle-sized were significantly higher than $lt; 3㎜ (p$lt;0.01).
After in vitro maturation, the rates reached to MI stage of $lt; 110㎛ oocyte groups(25%) was higher than 110-120㎛ and ≥120㎛ oocyte groups(11 and 10%) reached to the same stage(p$lt; 0.01), and the rates throughout MII stage of 110-120㎛ and ≥120㎛ and $lt;110㎛(70 and 76%) groups were higher than $lt; 110㎛(35%)(p $lt; 0.01).
When nuclear maturation rates were measured according to period, $lt; 6hr groups(7 and 10%) showed lower rates reached to Ml than ≥12hr groups(100%), 24hr groups(76%) revealed higher rates throughout MII than 18hr groups(40%).
These results indicate that the preparation of oocyte for the production of in vitro fertilization embryos and nuclear transplantation ones could be adapted, as follicle increased up to appointed size there was a corresponding increase in oocyte diameter, and differences of nuclear maturation rate revealed according to oocyte diameter and maturation period.
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