An investigation within a species (Gallus domesticus) of the hypothesis that embryonic and juvenile growth rates in birds are correlated

The hypothesis has been advanced from a study of several types of birds that the only way to alter growth rate in the juvenile is to alter the growth rate of the embryo. This was investigated within the species Gallus domesticus by comparing data from two pure lines (one with a slow and one a fast juvenile growth rate) and a broiler hybrid strain. Comparison of the data for the slow and fast line supported the general hypothesis. The incubation period was not significantly different in these two lines but the fast-line embryo was significantly heavier than the slow-line embryo throughout incubation. As a juvenile the fast-line chick grew almost twice as quickly as the slow-line chick to 8 weeks of age.