Transgenic pigs could lead to leaner pork

Although still in its relative infancy, transgenics is already offering an opportunity for researchers to aid organ transplants, produce drugs and enhance foodstuffs. The role of livestock in the culture of the post-modern world is being revised. Technology has always contributed to the definition of the interdependent relationship between man and livestock. As we begin to understand the genetics underlying the development and function of every cell, and develop technologies to manipulate the genetic program, this relationship will undergo another revolution.

Humans have long used animals as a source of medical compounds, including replacement hormones like insulin. Body parts, such as swine skin, have also been useful in medicine. In the near future, animals may produce life-saving pharmaceuticals in their milk that would otherwise be impractical to make or isolate. Livestock may be modified so that their organs don't induce immune rejection in humans and can therefore act as life-saving transplants. Products from animals, such as milk, meat and wool, may well have their composition or characteristics modified to make them more healthful and useful to man.

Toward this end, USDA/ARS scientists (Gene Evaluation and Mapping Laboratory, Bldg. 200, Room 8, BARC-East, Beltsville, MD 20705) believe that pigs genetically engineered with a growth factor gene may give consumers leaner pork in the future. While the research is in the basic stage, the new transgenic pigs carry a gene for insulin-like growth factor-I (IGF-I). Produced by ARS researchers in collaboration with colleagues at GeneMedicine Inc. (The Woodlands, TX), the pigs have some of the same positive carcass composition characteristics as transgenic pigs that have been injected with a growth hormone (GH) gene.

A key difference, however, is that none of the IGF-I pigs have developed the health problems previously encountered in the GH pigs. That's because most mammalian cells already have small amounts of IGF-I, which stimulates development of bone, muscle, nerve and organ tissues. IGF-I produced in muscle increases significantly without affecting the amount in other tissues, making these transgenic pigs unique.

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

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

Further information. Vernon Pursel; phone: [phone]; fax: [phone]; email: [e-mail].