FSH different regimes affect the developmental capacity and cryotolerance of embryos derived from oocytes collected by ovum pick-up in donor sheep

The objective of the present study was to compare the developmental capacity of sheep oocytes obtained by OPU after two different ovarian stimulations, and cryotolerance to vitrification procedures of in vitro derived embryos after in vitro maturation, fertilisation and culture of these oocytes. Sheep were divided into three groups: (A) no treatment (control); (B) constant doses of FSH (FSH-c); (C) decreasing doses of FSH (FSH-d). Ovine groups FSH-c and FSH-d were synchronised by the insertion of intravaginal sponges left in situ for 7 days; FSH (total dose: 96IU) was administered in four doses given every 12h starting on Day 5. Twelve hours after the last FSH administration oocytes were collected by OPU technique. The control group showed a significantly lower number ( P<0.05 ) of follicles (166) than FSH-c (294) and FSH-d (317) groups, while the number of follicles >5mm was significantly higher ( P<0.01 ) in FSH-d group, showing that this protocol stimulates the growth of a different follicle population compared to FSH-c group. The control group showed a higher number of <2mm follicles ( P<0.01 ). We did not find any difference in oocyte quality between the three groups and therefore the percentage of discarded oocytes was similar. No significant differences were found between control, FSH-c and FSH-d groups in terms of maturation (90.9, 85.7 and 87.7%, respectively) and fertilisation rates (75.2, 80.9 and 83.7%, respectively) while a significantly higher ( P<0.01 ) blastocyst rate was observed in the FSH-c group than in the FSH-d and control groups (20.4% versus 11.8 and 13.7%, respectively). After vitrification, warming and 72 h in vitro culture, the hatching rate was significantly higher ( P<0.01 ) in the control (87.5%) and FSH-c (90.5%) groups than in the FSH-d group (66.7%). Control and FSH-c groups showed a significantly higher ( P<0.001 ) number of total cells than FSH-d group ( 217.6+/-26.5 and 203.0+/-33.2 versus 147.5+/-20.2 ), while no differences were observed in ICM cell rates in the control ( 35.6+/-3.8 ), FSH-c ( 37.1+/-4.6 ) and FSH-d ( 36.6+/-6.7 ) groups. These results indicate that donor sheep stimulated with FSH-c produced better quality oocytes and blastocysts showing better cryotolerance than ewes given the decreasing doses treatment.