An International Team is Unraveling Swine Genetics

In times past, sea captains kept pigs on board their ships, but not to eat them. The captains believed pigs would unfailingly swim to the nearest shore if the ship went down — and thereby save the crew. Times have changed, but the pig is still viewed as a lifesaver, and again, not just for its food value — more than 40 pharmaceuticals are derived from swine.Scientists believe that with a little genetic tweaking, the pig could become even more useful — perhaps more feed thrifty, more disease resistant, or better adapted to biomedical research. Towards that end, they have created a nearly complete system of maps for the pig’s 18 pairs of non-sex chromosomes plus the X chromosome. Chromosomes are the threadlike structures in the nucleus composed of genes and other material.

These maps will help researchers to pinpoint where the pig’s 25,000 to 30,000 genes lie along the chromosomes, said Larry Schook, a professor at the Institute for Genomic Biology at Illinois, one of seven research centers in the United States and Europe which worked on the project. Independently, these researchers had compiled bits and pieces of the huge jigsaw puzzle that make up the pig’s genome. When they decided to collaborate, they pooled what they had, and then divided up the remaining research to fill in the blanks. When they got done, it was “like putting together an atlas of all the maps of all the roads in the U.S.,” said Schook. With an accurate map in hand, it’s much easier to pinpoint where genes are located on chromosomes. As science hones in on the complete picture of swine genetics, researchers can use the information to build a better pig. For instance, one goal of this work is to create pigs that grow big on less grain, which could help keep foods costs down and stretch limited grain supplies. But there are other potential advantages. “New DNA-based tools will be developed to identify and select genetically superior pigs that resist infectious disease and produce high quality and consistent cuts of meat,” said Deb Hamernick, national program leader with the U.S.D.A. Cooperative State Research, Education, and Extension Service. “Ultimately, pork producers will use DNA-based tools to select and manage animals based on an animal’s known genotype, which can be determined at birth.”

Unraveling swine genetics may also boost biomedical research. Pigs make ideal test subjects because they are much closer to humans in their makeup than are lab animals such as mice. The pig is used to research a range of conditions that afflict humans, including arthritis, obesity, and cardiovascular disease. Someday, the pig may provide a supply of organs for transplant into humans. “The pig genome is relatively similar to the human genome,” said Mark Boggess, Director of Animal Science at the National Pork Board in Des Moines, Iowa. “A lot of research that can’t be done in humans can be done in livestock, particularly in swine.”

A World to Feed

The race to produce a better pig is in part motivated by necessity. The world’s growing population needs to eat, and as incomes have risen in once poor parts of the world, demand for meat protein has been rising. Worldwide, meat consumption jumped more than 16 percent between 1995 and 2005.

But there’s a hitch. Rising meat production requires more grain to feed pigs, cattle, and chickens. However, the world’s supply of farmland has been eroded by development, and in the U.S. in particular, corn production has been increasingly diverted to produce ethanol. The shift of corn to ethanol has been especially damaging because it crimped corn supplies for animal feed and forced the price of feed up. “The hog industry is feeling a lot of pressure because of the diversion of corn to ethanol,” said Ronnie Green, National Program Leader in the Animal Production unit of the U.S.D.A.’s Agricultural Research Service.

Down the road, global warming could further impact grain production, worsening a difficult situation. “Global warming may change a lot of things,” said the Pork Board’s Boggess. This is where genetics comes in. With a genetic map in hand, pigs may be bred to gain weight with less grain, or they could be bred to digest and gain weight on types of feed they can’t eat now. Pigs may also be bred to withstand higher temperatures and other climatic changes brought on by global warming, Boggess said.

At the very least, understanding swine genetics would help hog producers tailor their feeding programs to pigs as they exist today. Producers already know there is a wide variation among domestic pigs in their ability to gain weight. But when pigs are born, hog growers don’t know which ones will gain weight easily and which ones won’t. “Right now, we can’t sort them so we treat them all the same,” said Green. This results in wasted feed.But someday, a simple genetic test given at birth may answer the question of which is which. “By knowing genetic variation, you could get rid of inefficient feed management,” said Green. “You’d use less feed. You’d get less manure.”

Globalization at Work

The project to map pig chromosomes succeeded only because a lot of institutions combined their research, said the Genomic Institute’s Schook. “The size of this project required an infrastructure that no one place had,” he said. “It required expertise that no one place had. If everybody had continued to do it by themselves, we would never have been able to do this. “We had independently started making these road maps of the pig chromosome. We had worked on them for five or ten years, and we had all taken different approaches. Then we said,‘if we pooled what we had, we could make a map of what’s missing.’ From there, we figured out what needed to be done to fill the holes. This is globalization at work.”

For more information: The full text of the pig gene research can be found in the August 2007 issue of the online journal Genome Biology under the title “A high utility integrated map of the pig genome."