Effect of follicular size on in vitro maturation, fertilization and culture of sheep embryos

A study was conducted to investigate the effect of follicular size (small، <2 mm diameter and large، ≥2 mm) on in vitro maturation، fertilization and culture of ovine oocytes. The ovaries (n=80) were collected from abattoirs in Srinagar city، India and transported in normal saline solution containing 5 μg gentamicin sulphate per ml in a thermos flask. The oocytes were collected by puncture technique and good and fair quality oocytes obtained were subjected to maturation in TCM-199 supplemented with epidermal growth factor (EGF) for 24 h under 5% CO2 and humidified atmosphere at 38. 5°C. The matured oocytes were then subsequently subjected to fertilization and culturing was done for six days. The results revealed that the maturation rate of large follicle oocytes (85. 20%) was higher than small follicle oocytes 52. 44%، P=0. 002). In vitro fertilization rates for small and large follicle oocytes were not significantly different (79. 54 and 76. 65%، respectively). However، cleavage and morula rates were higher in large follicle oocytes (58. 69 and 34. 13%) than small follicle oocytes (38. 63 and 19. 32%، respectively، P<0. 05). In conclusion، there is higher developmental competence of oocytes from the large follicles than small follicles and the pre-maturation of oocyte occurring during follicular growth is essential for subsequent embryonic development in sheep.