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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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