DIRECT AND CORRELATED RESPONSES TO LONG-TERM SELECTION FOR INCREASED BODY-WEIGHT AND EGG-PRODUCTION IN TURKEYS

Lines of turkeys were selected long-term for increased egg production (E line; 34 generations) or increased 16-wk BW (F line; 28 generations ). The E and F lines were started from randombred control populations (RBC1 and RBC2, respectively) that were also maintained to remove envi ronmental variation among generations. Realized heritabilities (h(2)) +/- SE in the E line, based on regressions of response on cumulated ac tual selection differentials (selection differentials weighted for the number of offspring produced), for 180-d and 250-d egg production wer e 0.34 +/- 0.02 (17 generations) and 0.26 +/- 0.13 (8 generations), re spectively. The realized h(2) of 16-wk BW in the F line was 0.26 +/- 0 .01. There was no consistent evidence of selection response reaching a plateau in either line. The genetic association of BW and egg product ion changed with selection in the E and F lines. The genetic correlati on varied from near zero to strongly negative and fluctuated between t hese extremes in both lines even though they started from different ba se populations and selection criteria differed. Other correlated respo nses to selection for increased egg production were increased average clutch length (intensity of lay), and decreased broodiness (total days lost), egg weight, shell coloration, and rate of response to stimulat ory lighting. Other correlated responses to selection for increased 16 -wk BW in the F line included: increased egg weight (due to increased albumen), longer eating bouts, and decreased average clutch length, se men production, walking ability, and resistance to Pasteurella multoci da and Newcastle disease virus, Selection within the E and F lines als o changed the frequency of MHC haplotypes and the changes appeared to be in opposite directions in the two lines.