This review presents the evolution and current possibilities, state of knowledge and prospects for in vitro production of pig embryos. Development of this technology for use in the international pig industry remains slow. IVP systems are generally comprised of three stage-specific culture environments: in vitro oocyte maturation (IVM), in vitro fertilization (IVF), and in vitro embryo culture (IVC). Hormonal supplements, such as FSH, eCG or hCG and follicular fluid, are added to the IVM medium in order to mimic the in vivo situation and stimulate nuclear maturation of the oocyte. Important elements are the cumulus cells that play a protective and metabolic role in oocyte cytoplasmic maturation. Efficiency of cytoplasmic maturation includes the ability of the oocyte to block the penetration of more than one sperm and also to support the decondensation of the sperm head within the ooplasm of the fertilized oocyte. The main feature, widely perceived to be a distinctive trait in porcine IVF, is the high prevalence of polyspermic fertilization. In the great majority of IVP studies on the pig, oocytes are harvested from the ovaries of prepubertal gilts out of necessity, due to the relative unavailability of adult sow ovaries. In fact, penetration rates exceeding 80% are typically achieved in prepubertal gilt oocytes, but polyspermy rates rarely measure less than 40%. When using sow oocytes, polyspermy rates in the range of 10% are routinely achieved. Instead, a number of porcine IVP groups routinely obtain a blastocyst formation rate of about 30% from in vitro matured oocytes, which is on par with that achieved in other farm animal species. Parameter for evaluating the success of a given porcine IVP system are also not without their pitfalls. Parameters used to define embryo quality include blastocyst morphology, total and inner cell mass, cell number, chromosomal abnormalities, metabolism, gene expression and apoptosis. One parameter of particular interest in the pig is apoptosis. The nuclear apoptotic features can be visualized using relatively simple fluorescent DNA-labeling techniques called TUNEL.
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