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 increased 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 populations 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 in 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 the time required for external pipping. The FL line had a longer period of incubation than the F line. Differences in the length of the incubation period 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 difference between lines in Trial 2. In Trial 3, the comparison of the F and RBC2 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 had a longer incubation period than the RBC2 line, whereas when the eggs were 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 line 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 the six lines. Overall regression of hatching time on egg weight and BW50 was positive for egg weight and negative for BW50. However, only 4% of the variation in the length of the incubation period could be explained by variation in egg weight and BW50. Within lines, the regression coefficient of length of the incubation period on BW50 was not significantly different from zero in any line but the sign was negative in five of six lines.