Quote: This is a phenomenon that I learned early in cattle selection classes. As more genes become homozygous, the animal doesnot grow as fast. NOw, I admit I do have a question about this, and that is, is the mature weight or size decreased also, and I think the answer is yes. THis is the foundation for the commercial lines to use cross breeding as it increses the rate of growth and the mature body size.
For example I bred a black sexlink rooster to my brown EE hen, she is my biggest EE. All stock from 2 hatcheries. THe three sons are HUGE, and outsized the father even to the novice eye. THe father grew up here and the sons grew up here. I can only credit hetersosis.
Sorry for jumping in; I"m behind on my reading and trying to catch up.