Broiler chickens are several times larger than those from the 1950s, and the reason is simple: genetics.
Martin Zuidhof of the University of Alberta did a study in 2005, when he was still with Alberta Agriculture, that compared breeds from 1957, 1978 and 2005. He and his team raised these three lines from hatching eggs to 56 days old.
“There was no difference in the feed they were given,” he said.
“We gave them all the same environmental conditions, the same litter and same access to water. You name it, it was identical.”
Pictures were taken at the end of every week to show the changes between the three lines. The 2005 line was much larger than the other two, which he said is because of genetics.
“We know that people don’t really trust or understand why chickens grow so fast,” he said.
“This is a way to show off that if the only thing that’s different between the groups of birds that we grow is their genetics, then we can clearly demonstrate that it’s not antibiotic feeding or growth hormones.”
Hank Classen, a professor in the University of Saskatchewan animal and poultry science department, agreed.
“It relates primarily to the short generation intervals between chickens,” he said. “We can select the best really quickly. It makes good progress for selecting chickens.”
Added Zuidhof: “We don’t see that same kind of progress in swine or beef because they don’t reach sexual maturity as fast and don’t have as many offspring.”
Karen Schwean-Larder, a professor of poultry science at the U of S, also agreed.
“Chickens have amazing genetic potential, and the groups that work in this area focus their energies on harvesting these potentials. The results have been amazing.”
All three professors said the changes in growth have nothing to do with growth hormones.
“I think people don’t want to change their opinion on how chickens are raised,” Zuidhof said.
“If you understand how this evolved over time, it’s not bizarre.”
Classen said selecting genes that make chickens grow larger is like a plant breeder making the best selections so they can get an increased yield.
“The sophistication of the breeding industry is very high,” he said.
Zuidhof said mistakes were made 20 to 30 years ago when chickens were selected just because they could grow fast and didn’t consider their ability to support their weight. That has changed, he added.
“The way broilers are selected now really has made for a robust and healthy animal.”