Ovarian physiology of prepubertal and adult animals is different. Some characteristics as follicular dynamics (follicular waves and growth) are similar but total follicular population and number of growing follicles are higher in prepubertal ovary. Prepubertal oocytes represent a negative model for in vitro studies since they lead to lower cleavage and blastocyst rates when they are used to produce embryos. This reduced ability to support embryonic development is due to follicular and oocyte differences. Follicular fluid and granulosa cells proteins, and steroidogenic potential differ between prepubertal and adult animals. Moreover, experiments using nuclear transfer demonstrate that cytoplasmic maturation of prepubertal oocytes is incomplete. These deficient oocytes are smaller, contain lower levels of MPF and MAP Kinase and differences in metabolism and cytoplasmic organelles are observed.