Gene Tweak Made Roosters Fat—and Infertile Leading to a shortage of chickens, and higher prices By Rob Quinn, Newser Staff Posted Jul 10, 2014 1:03 AM CDT 17 comments Comments The Ross roosters have been replaced by another breed. (AP Photo/LM Otero) (Newser) – The breed of rooster that sires around a quarter of America's chickens hasn't been getting the job done and a genetic tweak is to blame. Aviagen Group, the world's largest chicken breeder, made a change to the standard Ross male that has caused fertility issues, causing a shortage of birds and pushing up chicken prices, Reuters finds. The shortage has raised the price of chicken breasts by around 50 cents a pound at a time when consumers are also facing soaring beef and pork prices. At Sanderson Farms, the country's third-largest poultry producer, spokesman Mike Cockrell explains that the genetic change made the rooster very sensitive to overfeeding. "We fed him too much. He got fat. When he got big, he did not breed as much as he was intended to," Cockrell says. "The fertilization went way down, and our hatch has been way down." Aviagen has replaced the Ross breed with another kind to mate with the same hens, and the company says results have been favorable so far.