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New Transgenic Pigs with Lean Pork Potential

By Tara Weaver
February 18, 1998

Pigs genetically engineered with a growth factor gene may give consumers leaner pork in the future, Agricultural Research Service scientists say.

The new transgenic pigs carry a gene for insulin-like growth factor-I (IGF-I). The pigs were produced by ARS researchers in collaboration with GeneMedicine, Inc., of The Woodlands, Texas.

The IGF-I transgenic pigs have some of the same positive carcass composition characteristics as transgenic pigs previously injected with a growth hormone (GH) transgene. However, none of these IGF-I transgenic pigs have developed the health problems encountered earlier in the GH transgenic pigs.

IGF-I is a growth factor normally present in small amounts in most mammalian cells. It stimulates development of bone, muscle, nerve and organ tissues. IGF-I produced in muscle increases significantly without affecting the amount in the other tissues, making the IGF-I transgenic pigs unique.

The scientists injected the IGF-I gene into pig embryos soon after fertilization. They mated several IGF-I transgenic pigs to non-transgenic pigs to produce a second generation in which half the offspring inherited the transgene and half did not.

ARS scientists compared pigs with and without the transgene to see how IGF-I affected their growth rate, feed efficiency, carcass composition and general health. They compared those results with the results obtained earlier with the GH transgenic and non-transgenic pigs.

The researchers found the IGF-I transgene helped reduce carcass fat and boost lean body mass, making those hogs worth $6 more at market than control pigs without the IGF-I transgene. The study also confirmed that the IGF-I pigs didn't suffer from severe health problems associated with the GH transgene.

ARS scientists say this preliminary work is a first step to producing leaner pigs, but it will have to be tested on market-grade animals. Their next step will be to cross IGF-I transgenic pigs with market-line hogs to see if increased levels of the hormone enhance muscle development in already lean, heavy-muscled crossbred market hogs.

Scientific contact: Vernon G. Pursel, Gene Evaluation and Mapping Laboratory, Beltsville, Md., phone (301) 504-8342, fax (301) 504-8414,