DEVELOPMENTAL CAPACITY, ENERGY-METABOLISM AND ULTRASTRUCTURE OF MATURE OOCYTES FROM PREPUBERTAL AND ADULT SHEEP

Development to the blastocyst stage was assessed for oocytes obtained from prepubertal and adult sheep matured and fertilized in vitro. The proportion of cleaved oocytes reaching the blastocyst stage was signif icantly lower for oocytes derived from prepubertal sheep than for thos e from adult sheep (7.4% and 24.6% respectively). There were no differ ences in the metabolism. of glucose, glutamine or pyruvate between ooc ytes matured in vivo and in vitro, or of glucose or pyruvate between o ocytes from prepubertal and adult sheep. Glutamine metabolism by matur e oocytes from prepubertal sheep was significantly lower than that by oocytes from adult sheep. Ultrastructural studies revealed no differen ces in the morphology of cytoplasmic organelles of oocytes matured in vitro from prepubertal and adult sheep, but differences in the volume fraction and size of mitochondria and cortical granules were observed. These data suggest that mature oocytes from prepubertal sheep do not possess the developmental potential of their adult-derived counterpart s, and this phenomenon may be associated with metabolic and ultrastruc tural anomalies.