Ten years ago, Dr. Gerry Havenstein at North Carolina State University did a careful study of weight gain in chickens, comparing (under identical conditions) a modern 21st-century breed with a 1957 breed that had been kept going. He found that, at six weeks of age, the modern chicken was six times as heavy and had 9% more breast meat. Of that improvement, he found, 85% came from genetics and only 15% from better feed.
By 2001, when the study was done, a chicken reached the weight at which it would be killed in one-third of the time and after eating one-third of the food compared with the 1957 breed. That represents a considerable reduction in waste and in the amount of land devoted to growing feed per chicken.
In the decade since, there has been a consistent and linear increase in both weight gain and food-conversion efficiency in the broiler industry. Outside the lab, on the farm, chickens have accelerated their daily rate of growth by about 0.89 grams per year.
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