Selection for Body Weight at Eight Weeks of Age

CORRELATED responses, or the associated changes of unselected characteristics which occur during artificial selection for a particular trait are due to environmental influences, genetic effects and a combination of the two. The theoretical aspects of correlated responses and procedures for the estimation of phenotypic, genetic and environmental correlations have been recently reviewed by Lerner (1958) and Falconer (1960). Although considerable research has been published on the growth of chickens, little is known about the associated changes which occur in unselected characteristics when artificial selection is made for growth to a particular age. Schnetzler (1936) found that two generations of selection for fast and slow growth to eight or nine weeks of age influenced adult body weight, egg weight and chick size. Maloney and Gilbreath (1962) observed that ten generations of selection in opposite directions for 12-week weight resulted in differences between the lines for 6-week weight, egg weight, age at…