The dramatic increase in growth is mirrored by a much shorter time needed to bring chickens to market today. In 1955, it took 70 days to let a chicken mature to sell for meat. Now, it takes just 47 days.
The poultry industry argues that bigger chickens means that fewer chickens need to be killed to produce the same amount of meat. But what effect is this extra mass having on the chickens themselves?
Martin Zuidhof, one of the authors of the study acknowledges that with greater size comes health problems for chickens.
"Twenty-five years ago was probably the low point in the industry in terms of negative consequences of selection," he told CTV News. "There were metabolic disorders, heart attacks, just difficulties that were associated with rapid growth."
But according to Paul Shapiro, Vice President of Farm Animal Protection of The Humane Society of the United States, that problem is far from solved.
"Chickens in the meat industry are sentenced to a lifetime suffering because of genetic manipulation that forces them to grow so rapidly," he told The Dodo. "All you need to do is go look at a shed of broiler chickens more than a month old. Most have difficulty walking and often collapse under their own weight."