Growth to sexual maturity of dwarf and nondwarf White Rock chickens divergently selected for juvenile body weight.

Growth from hatching to the onset of lay (sexual maturity) was studied in White Plymouth Rock pullets from lines selected for high (HN) and low (LN) 56-day body weight, their reciprocal F1 crosses, an F2 cross, and two dwarf populations originating from the HN and LN parental lines. The highest R(2)s for describing growth for all populations except HN were obtained when body weight was expressed relative to body weight at sexual maturity. Modes of inheritance differed depending on whether patterns of growth were expressed in a chronological time frame or on a physiological basis. Heterosis observed for age at sexual maturity and for body weight after the age when selection was made was not in evidence when ages and weights were expressed as a proportion of those at sexual maturity.