The domesticated chicken has been a source of meat and eggs for humans for at least 8,000 years. But for a handful of researchers at Virginia Tech, who with their colleagues around the world have decades of research in genetic studies of animal domestication under their belts, the domesticated chicken is helping better understand everything from animal appetites to genetics.
After joining the Virginia Tech faculty in 1957, Paul Siegel, University Distinguished Professor Emeritus of Animal and Poultry Sciences in the College of Agriculture and Life Sciences, devised a simple experiment that continues to this day.
That experiment was to develop two distinct lines from a common founder population of White Plymouth Rock chickens based on their weight at eight weeks from hatching. Every generation, he bred the heaviest and lightest chickens within their respective lines, thus establishing a high-growth and a low-growth group.
Today, Siegel’s high-growth chickens dwarf their low-growth counterparts, weighing on average 10 times more by the time they reach the eight-week selection age.
Siegel describes his experiment as one of resource allocation.
“A population has to be balanced,” he said. “If we move one of the factors such as growth, reproduction, or immunology in one direction, the others will move in another direction. By selecting for growth, we are testing the genetic and immunological limits of poultry.”
Several Virginia Tech animal scientists have been able to utilize the high- and low-growth chicken lines over the years to advance their research projects.
Michael Denbow, a professor of animal and poultry sciences, has been using them to understand how the brain regulates food intake -- a significant issue in Siegel’s line bred for extreme growth. He is testing several compounds to see what effect they have on the brain’s ability to determine whether the body has enough energy.
“Interestingly, pharmacological systems that affect food intake in mammals act the opposite in chickens,” he said. “We have to find out why to have a complete understanding of growth in poultry.”
According to Denbow, if producers can introduce a compound into the food or water used at their chicken operations, they might be able to influence the chickens’ food intake and, therefore, the productivity of the farm.
Meanwhile, Ron Lewis, an associate professor of animal and poultry sciences, has studied the change that Siegel’s selection process has caused over time in an attempt to provide a simple understanding of the dynamics of the chicken populations.
“We are tracing ancestral information about these high- and low-growth chickens and taking a probabilistic approach to see how the lines changed over time,” Lewis said.
He said he hopes to track down the consequences of selection on effective population size. “I am interested in how many distinctive individuals over time a line must have to allow changes in that population due to selection to continue.”
Also studying poultry genetics, Eric Wong, the John W. Hancock Professor in Animal and Poultry Sciences, has investigated gene expression of nutrient transporters in Siegel’s chicken lines. In particular, he explored the expression of a series of amino acids and peptide transporters responsible for growth and nutrient management.
“We asked ourselves, ‘Does the expression of nutrient transporters play a role in the extraordinary growth in these poultry lines?’ ” Wong said. “We found that the answer was no. In fact, the high-weight birds had a lower expression and were able to assimilate nutrients efficiently.”
Despite the results, Wong and his students closed one door of research and opened another.
The scientific community at large has benefited from the research done on the high- and low-growth chicken lines just as much as Virginia Tech faculty members have. Last year, an article in the scientific journal Nature highlighted a breakthrough in genetic studies of animal domestication, thanks in part to these two lines.
The research team identified a gene found in all of Virginia Tech’s high-growth chickens, but few of the low-growth ones, that appears to regulate appetite. The finding could have ramifications for both animal and human health studies involving weight. The Virginia Tech poultry lines, which include the complete pedigree of 53 generations, might even provide clues about certain human health disorders such as obesity and anorexia nervosa.
In addition, the team may have found a genetic mutation in poultry caused by animal domestication, the first such discovery of its kind.
In January 2010, the American Poultry Historical Society inducted Professor Paul Siegel into the American Poultry Industry Hall of Fame for his years of service to students, colleagues, and industry officials.
When reflecting on the poultry industry’s highest honor, Siegel did not mention his long list of research accomplishments. Instead, he recalled the support of his teachers, students, colleagues, and family.
“In my mind, my main legacy is my students,” he said.
In fact, more than 50 students have completed a graduate degree under Siegel’s supervision, some of whom are now leaders in science and industry.
About 10 years ago, Virginia Tech researchers intercrossed the high- and low-growth chickens to determine which traits remained in the gene pool and which did not. This third line has helped researchers understand the underlying process that takes place during breeding.
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