K. E. Nestor1, J. W. Anderson, and R. A. Patterson
The Ohio State University Department of Animal Sciences
A line (F) of turkeys was selected over 30 generations for increased 16-week body weight. The base population for the F line was a randombred control population (RBC2) that was maintained along with the F line without conscious selection. In order to study the effects of selection on genetic parameters, the effect of selection on selected and correlated traits in the F line was studied, whenever possible, at 10-generation intervals (1 to 10, 11 to 20, and 21 to 30) and over all generations (1 to 30). Values of the F line were expressed as deviations from the RBC2 line in order to remove yearly environmental variations.
Selection was effective in increasing 16-week body weight in the F line. Selection differentials based on the mean of selected parents minus the mean of the entire population (intended) and intended selection differentials weighted for number of offspring produced (actual) did not consistently differ, indicating that natural selection was not opposing artificial selection. The realized heritability (h2; ratio of genetic variation to total variation in a trait) of 16-week body weight in the F line based on the linear regression of selection response on accumulated actual selection differentials declined with selection, and the decline appeared to be slightly different for males than females. For both sexes combined, the realized h2 was 0.309 ± 0.022 (standard error), 0.268 ± 0.033, 0.242 ± 0.026, and 0.254 ± 0.007, respectively, for Generations 1 to 10, 11 to 20, 21 to 30, and 1 to 30.
Genetic increases in 16-week body weight in the F line were positively associated with body weight at other ages (8, 20, and 24 weeks of age and at 50% egg production), days from stimulatory lighting to production of the first egg, and egg weight, and negatively associated with egg production, intensity of lay (maximum and average clutch length and rate of lay), and hatch of fertile eggs. There was no significant relationship of 16-week body weight and total days lost from broodiness or fertility. Genetic changes in some correlated traits were not consistent in all generation intervals studied, indicating that the genetic correlation between the selected trait (16-week body weight) and the correlated trait changed with selection.
1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 125 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH 44691, 330-263-3757, Fax 330-263-3949, e-mail: nestor.1@osu.edu