The ability to produce pig embryos in vitro (in the laboratory environment) has been mastered at Mississippi State University.
Pig oocytes (immature egg cells) are matured in the laboratory and fertilized. The resulting embryos develop from a single-cell stage to 2-, 4-, 8-cell and until the blastocyst, the most advanced stage, before being transferred to a recipient sow or gilt.
The benefits of this technology are multi-fold — it increases reproduction efficiency, accelerates genetic improvement, offers certain pig health advantages and provides important means for biomedical research.
To accomplish in vitro production (IVP) of embryos, oocytes were first aspirated from follicles 2-6 mm. in diameter from ovaries harvested at a slaughterhouse. Only oocytes with several layers of cumulus cells were collected under a microscope. After three washes in a special media, the oocytes were matured under 5% CO2, at 39°C (102°F) in a humidified tissue culture incubator for 44 hours.
The matured oocytes were then placed into fertilization media and in vitro fertilization was performed using percoll separated live sperm from freshly collected boars. Fifty oocytes in 500 microliters of fertilization medium were incubated with 500,000 spermatozoa for five hours.
Once the in vitro fertilization was completed, cumulus cells around the oocytes and the spermatozoa were removed from the fertilized oocytes, now called zygotes. The zygotes were then placed into embryo culture media for six days with the addition of 10% fetal bovine serum on Day 4 after fertilization.
Researchers tested two of the most widely used commercial embryo culture media (PZM-3 and NCSU-23) for their ability to support embryo development to blastocyst stage. The experiments were repeated more than four times with about 900 oocytes for each media.
Results showed that PZM-3 media supported higher embryo development to blastocyst stage than did the NCSU-23 media (20% vs. 6%).
These in vitro-produced embryos can be successfully transferred to hormonally prepared recipient sows or gilts, although successful pregnancy rates are less efficient than natural breeding or artificial insemination.
The IVP of pig embryos make it possible to propagate genetically superior sows and boars much faster. The value of these genetically superior pigs can be extended through cloning, followed by in vitro culture of the embryos and embryo transfer. Animal genomes can be modified (genes added or removed), making them valuable for biomedical research, production of biopharmaceutical proteins in pigs and, possibly, for the production of organs for human transplantation.
Researchers: Hongfeng Wang, Tribetta Spires and Erdogan Memili, Mississippi State University. Contact Memili by phone (662) 325-2937 or e-mail: em149@ads.msstate.edu.