Document Type : Original Article
Theriogenology Department, Faculty of Veterinary Medicine, College of Veterinary Medicine, Urmia University, Urmia, Iran
Anatomy Department, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
An evaluation of the developmental competence of vitrified mouse germinal vesicle (GV) oocytes with various equilibration and vitrification times; in the presence or absence of cumulus cells and by comparison between the cryotop method and straws was performed.
Materials and methods
Mouse GV oocytes were considered in cumulus-denuded oocytes (CDOs) and cumulus-oocyte complexes (COCs) groups. Their survival and developmental rates were studied in the following experiments: (I) exposure to different equilibration times (0, 3 and 5 minutes) and vitrification (1, 3 and 5 minutes) without plunging in LN2 as toxicity tests, (II) oocytes were vitrified using straws followed by exposure to equilibration solution for 0, 3 and 5 minutes and vitrification solution for 1 and 3 minutes, and (III) oocytes were vitrified by cryotop following exposure to equilibration for 5 minutes and vitrification for 1 minute, respectively.
Maturation and developmental rates of the COCs were higher than CDOs in the nonvitrified group (p<0.05). The survival and maturation rates were low in all oocytes exposed to vitrification solution for 5 minutes (p <0.05). In vitrified CDOs and COCs using straws, the survival rates ranged from 56.9% to 85.4% and 44.0% to 84.5%, and the maturation rates from 35.3% to 56.8% and 25.8% to 56.2%, respectively; which were lower than non-vitrified samples (p <0.05). Cryotop vitrified oocytes showed higher survival, maturation and fertilization rates when compared to straw in both CDOs and COCs (p <0.05).
The presence of cumulus cells improves developmental competence of GV oocytes in control groups but it did not affect the vitrified group. Vitrification of mouse GV oocytes using cryotop was more effective than straws, however both vitrification techniques did not improve the cleavage rate.