Incubation Period of Chickens Selected Bidirectionally for Juvenile Body Weight

BIDIRECTIONAL mass selection for body weight at eight weeks of age (Siegel, 1962) has resulted in concomitant changes in embryonic stage at oviposition (Coleman and Siegel, 1966) and development during incubation (Coleman et al., 1963). The diameter of the blastoderm of unincubated eggs and the number of somites after 38 hours of incubation are influenced by inbreeding and outbreeding (Bernier et al., 1951). Smyth and Howes (1949) demonstrated that the length of the incubation period could be changed through artificial selection, and Crittenden and Bohren (1961) reported that hatching time was highly heritable. Further, Henderson (1950) observed differences among breeds for the length of the incubation period. Henderson and Champion (1948) noted that juvenile weights of chicks that hatched early were somewhat heavier than their later hatching contemporaries. Since our weight lines are known to differ in embryological stage at oviposition, it is of interest to determine if the length . . .