Influence of selection for increased body weight, egg production, and shank width on the length of the incubation period of turkeys

An experiment was designed to study the influence of selection for increase d 16-wk BW (F line), egg production (E line), and shank width (FL line) in turkeys on length of the incubation period and to estimate the influence of adult BW (BW50) and egg weight on the incubation period. The base populati ons for the F, FL, and E lines were randombred control (RBC)2, F, and RBC1, respectively. An additional RBC (RBC3) was also included in the study. The experimental turkey lines differed in length of the incubation period i n all trials, indicating genetic differences exist. The E line, in general, had a longer incubation period than the RBC1 line, due to an increase in t he time required for external pipping. The FL line bad a longer period of i ncubation than the F line. Differences in the length of the incubation peri od between the F and RBC2 lines were inconsistent. The F line had a shorter incubation period than the RBC2 line in Trial 1, whereas there was no diff erence between lines in Trial 2. In Trial 3, the comparison of the F and RB C2 lines was influenced by treatment of the eggs prior to setting. When the eggs were held at room temperature for 29 h prior to setting, the F line h ad a longer incubation period than the RBC2 line, whereas when the eggs wer e set directly from the egg cooler, there was no line difference. The line differences in length of the incubation period could not be explained by li ne differences in egg weight based on a comparison of line means for these traits. Within lines, the regression of length of the incubation period on egg weight was positive and significantly different from zero in three of t he six lines. Overall regression of hatching time on egg weight and BW50 wa s positive for egg weight and negative for BW50. However, only 4% of the va riation in the length of the incubation period could be explained by variat ion in egg weight and BW50. Within lines, the regression coefficient of len gth of the incubation period on BW50 was not significantly different from z ero in any line but the sign was negative in five of six lines.