Oocytes attain developmental competence as a result of their maturation, which gives them nuclear and cytoplasm maturity. In physiological conditions the developmental competencies of oocytes are achieved in the environment of ovarian follicles before ovulation. In in vitro conditions, however, this occurs in a culture medium which, for porcine oocytes, is generally a TCM-199 and NCSU-23 medium supplemented in specific proportions of amino acids, proteins, hormones, growth factors and follicular fluid. The specific nature of porcine oocytes is that it takes them almost twice as long to obtain nuclear and cytoplasm maturity as in the case of other species of farm animals. Moreover, a common problem of in vitro maturation is the absence of normal cytoplasm maturity. Irregularities in translocation of mitochondria in the cytoplasm and transferring ions signals may also be observed. The absence of cytoplasm maturity of oocytes on the other hand reduces the possibility of male pronucleus (MPN) formation and development of zygotes to the blastocytes stage. Therefore, the latest studies concentrate on formulating methods of in vitro culture which enable normal development of porcine oocytes both in their nuclear as well as cytoplasm maturity.
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