Genetics of growth and reproduction in the turkey. 14. Changes in genetic parameters over thirty generations of selection for increased body weight

A line (F) of turkeys was selected over 30 generations for increased 16-wk BW. The base population for the F line was a randombred control population (RBC2) that was maintained without conscious selection and used to remove y early environmental variation in the F line. Selection was effective in inc reasing 16-wk BW in the F line. Selection differentials based on the mean o f selected parents minus mean of entire population (intended) and intended selection differentials weighted for number of offspring produced tactual) did not consistently differ, indicating that natural selection was not sign ificantly opposing artificial selection. The realized heritability (h(2)) o f 16-wk BW in the F line, based on the linear regression of the selection r esponse on accumulated actual selection differentials, declined with select ion; the decline appeared to be slightly different for males than females. For both sexes combined, the realized h(2) was 0.309 +/- 0.022 (SE), 0.268 +/- 0.033, 0.242 +/- 0.026, and 0.254 +/- 0.007, respectively, for Generati ons 1 to 10, 11 to 20, 21 to 30, and 1 to 30. Genetic increases in 16-wk BW in the F line were positively associated with BW at other ages (8, 20, and 24 wk of age and at 50% production), days from stimulatory lighting to pro duction of the first egg, and egg weight. Genetic increases were negatively associated with egg production, intensity of lay (maximum and average clutch length and rate of lay), and hatch of f ertile eggs. There was no significant relationship between 16-wk BW and tot al days lost from broodiness or fertility. The genetic changes in some corr elated traits were not consistent in all generation intervals studied, indi cating that the genetic correlation between the selected trait (16 wk BW) a nd the correlated trait changed with selection.