New route to big pigs

Two pigs at 45 days post-injection (modified on right)

Scientists have developed a new method of boosting the size of pigs which appears to avoid the sometimes debilitating side effects seen with more conventional treatments.

The researchers have used a genetic modification that can make young animals grow faster and more than 20% bigger.

In many countries, farmers currently inject a growth hormone to increase the size of their pigs. But because the hormone is rapidly broken down in the animals' bodies, frequent injections are often required to bolster the growth-promoting effects.

More seriously, the hormone can lead to abnormal growth with problems such as enlarged organs and skeletal defects. Some animals are so malformed they cannot stand up.

The situation has drawn fire from animal welfare groups and the European Union, which is in dispute with the US over hormone-treated meat.

Human diseases

Now, researchers led by Professor Robert Schwartz from the Baylor College of Medicine in Houston believe they have found a technique that will avoid the problems seen with conventional treatment. They even think it could provide new options for patients undergoing growth-hormone replacement therapy for conditions such as dwarfism or osteoporosis and help prevent muscle deterioration in Aids and cancer patients.

The key to the new technology is getting the pigs to make large quantities of growth hormone in their own bodies.

Two-week-old animals were injected with DNA that coded for an altered hormone that cannot easily be broken down by proteins in the body. The DNA also included a synthetic promoter that ensured high levels of the hormone were produced in the muscle cells.

In their experiments, which are reported in the scientific journal Nature Biotechnology, the injected pigs were 22% heavier than untreated animals after 65 days and showed no signs of side effects.

The treated pigs ate 25% less feed and were ready for slaughter two weeks earlier. The animals also produced less manure - something which has become a major environmental issue.

Professor Robert Schwartz said additional research would have to be done to show that the meat was safe for human consumption, and the treatment had no negative long-term impact on the animals. The technique would then have to be approved by the US Food and Drug Administration before it can be used commercially.

"We think that over the long term this is going to be a defining technology that will change the face of how agriculture is done,'' Professor Schwartz said.

Consumer reaction

"This is extremely interesting work, but it has some problems with how the consumer will receive it,'' said Max Rothschild of Iowa State University, one of the leading authorities in the US on pig genetics.

"Will consumers eat animals that are treated in such a fashion. The jury is still out. ... In Europe, the answer is absolutely not.''

It would be far less controversial to continue improving pigs by identifying genes that control growth and other traits, he said.

Rebecca Goldburg, senior scientist for the US Environmental Defense Fund, said: "I don't think most consumers are very interested in eating hormone-treated meats.

She said it would take considerably more research to prove the technology was safe for both pigs and humans.

"I'm not confident that these pigs will be as healthy as pigs without the hormone. Animals as a whole are less plastic than plants. When their systems are disturbed by genetic engineering, their whole system can go out of whack.''