Selection for Body Weight at Eight Weeks of Age

Abstract

BIDIRECTIONAL selection experiments for juvenile growth of chickens have demonstrated that mean body weight at time t may be readily changed beyond the limits of the base population (Schnetzler, 1936; Maloney et al., 1963; Gyles and Thomas, 1963). Lacking, however, is information concerning changes that occur in factors influencing growth. Some attempts have been made to investigate the nutritional physiology of the lines derived from the two-way selection experiment for eight-week weight by Siegel (1962). Siegel and Wisman (1962) observed that decreases in protein and energy levels below that at which selection was practiced reduced body-weight gains for males and females in both lines. Protein and energy levels above those employed during selection resulted in increased growth responses for males of both lines but not females. Subsequently, Wisman and Siegel (1963) defined more precisely the protein and energy requirements for males and females in these lines. The data in both …