Title: RECENT DEVELOPMENTS IN THE GENETIC ENGINEERING OF LIVESTOCK SPECIES
Bolt Douglas J,
Soloman Morse B,
Submitted to: Nutrition International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 1, 1994
Publication Date: N/A
Interpretive Summary: Mammalian transgene expression, despite the low rate of gene integration and expression has markedly improved production performance in some lines of pigs. This enhanced performance additionally results in meat of improved composition from a human diet-health perspective. Reduced total lipid and a shift in fatty acids with a greater polyunsaturaed content are desirable characteristics. This benefit occurs without compromising meat tenderness. Future research will concentrate on tissue-specific transgenes expression and better regulation of expression. Of the limited transgene available for research, results on meat quality for non-growth related transgenes are unknown.
Microinjecting foreign DNA into the pronucleus of fertilized ova is the predominant method employed to produce transgenic animals. The goal of our research using this approach is to improve productivity traits, enhance animal health and produce useful human health products. In cattle, pigs and sheep, the foreign DNA (transgene) integrates into the genome of only .1 to 4.5% of gene-injected embryos and the transgene is expressed in only about 60% of those animals. Despite low integration and expression efficiency, improved production traits have been realized using structural transgenes for GH, GRF, IGF-1 and the cellular SKI oncogene. Some transgenic pigs have demonstrated improved rate and efficiency of body weight gain and have had reduced intra-, inter- and extra-muscular fat. In addition, some transgenics have had a more desirable molar ratio of saturated:mono-:poly-unsaturated fatty acids (approaching 1:1:1, which many believe to be ideal in human diets). These advantages in meat composition have not come at the expense of meat tenderness. Transgenic pigs expressing growth related transgenes are generally unthrifty and numerous health defects, a problem that must be understood and corrected before this technology can be applied to production agriculture. Research is also needed to improve integration efficiency and to construct transgenes whose expression is easily regulated. However, transgenic technology may provide livestock producers in the future with a faster and more predictable technique to make genetic progress and meet consumer needs than classical population selection methods.