GENETIC ANALYSES OF INCUBATION-TIME IN WEIGHT-SELECTED LINES OF CHICKENS AND THEIR CROSSES

Incubation time was evaluated in lines of White Plymouth Rock chickens selected for high (HW) and low (LW) 8-week body weight, their reciprocal F1 crosses (HL and LH) and F2 populations which were produced by inter se mating of F1 cross HL (HLHL) and by inter se mating of F1 cross LH (LHLH). Independent, random samples of eggs from each population were examined every 8 hours for days 18 through 21 (hours 408 to 504) of incubation. Perinatal stages recorded were % pipped through the air cell, % pipped through the shell and % hatched. Hours of incubation at which 25, 50 and 75 % of each population were at each perinatal stage were calculated. Line LW chickens pipped through the air cell, pipped through the shell and hatched approximately 12, 7 and 5 hours earlier than line HW chicks, respectively. Difference between the reciprocal F1 crosses and similarity between HL embryos and their LW dam line embryos suggested maternal influence for incubation time. Heterosis with respect to F1 cross HL was highly significant for all traits measured but was not significant with respect to F1 cross LH. Recombination effects were nil for all traits measured.