Researchers at the Univ. of Alberta found that chickens have become more efficient at converting their feed. Their findings were published in the journal Poultry Science.
The researchers examined three types of chickens: Two Univ. of Alberta Meat Control chickens that were unselected since 1957 and 1978; and Ross 308 chickens that were more recently bred to select for certain traits. Researchers photographed front and side profiles of eight birds per strain, and data on the chickens' "growth rate, feed intake, and measures of feed efficiency including feed conversion ratio, residual feed intake, and residual maintenance energy requirements" were collected.
"From 1957 to 2005, broiler growth increased by over 400 percent, with a concurrent 50 percent reduction in feed conversion ratio," the study authors wrote.
Breast meat yield increased by 79 percent in male chickens and 85 percent in female chickens, the researchers found. The study authors said that over a period of 50 years of selecting for specific traits, producers have achieved beneficial changes such as larger breast size. There also were unintended changes the researchers noted.
"Unintended changes such as enhanced sexual dimorphism are likely inconsequential, though musculoskeletal, immune function, and parent stock management challenges may require additional attention in future selection programs," the authors wrote.