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Unintended Effects of Genetic Manipulation
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Sheep growth hormone expression was highly variable in transgenic pigs, whose bodies had more protein and water and less fat.

Manipulated Organism: Pig (Sus domesticus).

Inserted Transgenes: Sheep (ovine) growth hormone gene, with expression controlled by the ovine metallothionein promoter.

Goal of This Study: Compare the development of pigs expressing sheep growth hormone with non-GM pigs from the same stock.

Results of This Study:
  • Four hundred eggs were recovered from bred pigs, injected with transgenic DNA, and then implanted in 17 pigs along with 50 eggs that had not been injected with transgenic DNA. These animals gave birth to 109 pigs, 15 of which tested positive for the transgene. Of the 15 transgenic pigs, 3 died soon after birth, so only 12 were available for further study.

  • Of the 12 transgenic pigs, 6 had no detectable amount of ovine growth hormone (oGH) in their blood, 5 had high levels of oGH, and 1 had a low level of oGH that increased 20-fold when the pig was fed a zinc supplement. The promoter used with the transgene (metallothionein) was supposed to increase expression in the presence of zinc, but this response was only observed in the one transgenic pig.

  • The transgenic pigs with elevated oGH levels did not grow more rapidly than the non-GM cohort during the 9-week study, but their body composition was quite different. Whereas the carcasses of the non-GM pigs contained 26% fat, the GM pigs had only 5% fat. The GM pig carcasses contained more protein and water to produce a similar total weight.

  • The GM pigs also had livers, kidneys, and adrenal glands that were 2-3 times heavier.

Source: Pursel, V. G., R. J. Wall, M. B. Solomon, D. J. Bolt et al. (1997). "Transfer of an Ovine Metallothionein-Ovine Growth Hormone Fusion Gene into Swine," Journal of Animal Science vol. 75, pp. 2208-14.

Author Affiliations: USDA Agricultural Research Service, Beltsville, MD; University of California, Davis; CSIRO Australia.

Funding: Not mentioned.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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