California State University Agricultural Research Initiative Final Report, February 26, 2006.
Producers of domestic livestock strive to improve genetic influences in their herds. This requires identification, and propagation of animals that demonstrate desirable characteristics. The more animals available from which to select, the greater the opportunity to discover high-performance animals. Predetermination of the sex of offspring would provide a greater number of males or females from which to select the top individuals that will contribute the genetics to the next generation. Many attempts at sexing semen and identification of sex in preimplantation embryos have been mildly successful. However, recent advances in gene amplification enable investigators to use sex-specific probes to determine sex in only 1 cell removed from embryos. The biopsy method has had variable success in fresh embryos. However, manipulation of cryopreserved embryos reduces viability of the embryos (Bredbacka, 1998). Therefore, novel approaches to improve pregnancy rates may result in effective reproductive rates. One such approach is to vary the number of manipulated, cryopreserved embryos transferred into each recipient to increase the chances of successful pregnancy. The research performed identified the most successful techniques to biopsy and sex embryos using the mouse as a model animal. DNA from collected cells was amplified using polymerase chain reaction (PCR) or sex specific probes to determine sex. Secondly, the most effective techniques were applied to cattle embryos and survival rates in micromanipulated, cryopreserved embryos were determined. Finally, recipients were implanted with one or two embryos that sex had been previously determined. Pregnancy rates, including the incidence of twinning, were recorded. The hypothesis tested was: a single method for sexing bovine cryopreserved embryos can yield high accuracy and high pregnancy rates for the desired sex.
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