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 In vitro production of porcine embryos and their cryopreservation

　

Takashi Nagai¹,², Tamas Somfai³, Kazuhiro Kikuchi⁴, Koji Yoshioka⁵ and Naomi Kashiwazaki⁶

　

¹Food and Fertilizer Technology Center (FFTC), Taipei 10648, Taiwan 

²Seoul National University, Seoul 151-742, Korea

³NARO Institute of Livestock and Grassland Science, Tsukuba, Ibaraki 305-0901, Japan

⁴National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan

⁵National Institute of Animal Health, Tsukuba, Ibaraki 305-0856, Japan

⁶Azabu University, Sagamihara, Kanagawa 252-5201, Japan

　

e-mail: taku@fftc.org.tw

　

ABSTRACT

　

    With the increase in worldwide demand for meat, fast-growing species with efficient feed conversion rates – such as pigs – are likely to account for a major share in the growth in the livestock subsector. The increase in animal numbers is not spread evenly round the globe: Asia leads the increase, whereas pig numbers in North America and Europe are increasing more slowly or holding steady. In Africa, pig numbers have recently grown more rapidly, reflecting increased adoption of pig husbandry in a continent where “livestock” has traditionally been taken to mean “ruminants”. .Actually pigs have been playing an important role in meat production in many countries, especially in Asia. They produced the most important source of meat (40%) followed by cattle (29%). As a result commercial pig production has intensified significantly in recent decades. More pigs of the same few breeds are kept on fewer farms, with increased output of animal products; under human selection force, only economically efficient breeds are receiving enough care from human beings while the other ones have been ignored and are facing major population loss. This leads to the fact that as many as 47 breeds are categorized as critical, another 85 breeds are endangered, and 151 breeds have become extinct. These statistics show clearly the serious loss of porcine bio- and genetic diversity.

　

    Systems for the in vitro production (IVP) of porcine embryos have advanced to the stage where large numbers of embryos can be reliably generated from the oocytes collected from abattoir-sourced ovaries or ovaries obtained by operation in a single production run. These systems are extremely useful for embryo cryopreservation. Especially IVP of porcine embryos combined with cryopreservation of resultant embryos are important technologies for gene banking in pigs; cryopreservation of embryos and oocytes offers the possibility for the preservation of female genetic lines. However, while the efficiencies of these systems are generally considered to be acceptable, a number of issues remain. Following oocyte in vitro maturation and fertilization, polyspermic fertilization remains to be a problem and the viability of IVP embryos is poor compared with in vivo derived embryos. Furthermore, despite recent advances in the in vitro culture of pig embryos, the conditions used are still considered to be sub-optimal. The need for high quality IVP embryos for the generation of pigs even after cryopreservation continues to drive improvements in the efficiency of IVP and cryopreservation systems, as well as the procedures used to transfer embryos into recipients. Recently our researches have demonstrated that IVP embryos can be both selected for monospermy and vitrified effectively at the zygote stage and their direct transfer into recipients is an effective approach to overcome the problems of polyspermic fertilization and in vitro culture stress. Regarding oocyte cryopreservation, our researches have revealed that using current protocols, vitrification of porcine oocytes at the immature stage is more advantageous compared with vitrification at the matured stage since oocytes preserved at the immature stage show better developmental competence in the IVP system. Coupled with the improvements in oocyte and embryo cryopreservation, the IVP of porcine embryos for breeding and conserving rare pigs may become feasible in the near future.

　

Keywords: Pig, Gene Banking, Cryopreservation, In Vitro Production, Vitrification, Embryo, Oocyte

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