CORRELATED RESPONSES TO LONG-TERM DIVERGENT SELECTION FOR 8-WEEK BODY-WEIGHT IN CHICKENS - GROWTH, SEXUAL MATURITY, AND EGG-PRODUCTION

Thirty-six generations of divergent selection for BW at 8 wk of age (B W8) resulted in approximately an eightfold difference between the high (HWS) and low (LWS) lines for this trait. Correlated traits included BW at 4, 24, and 38 wk of age (BW4, BW24, BW38, respectively), age at first egg (AFE), and percentage hen-day egg production (HDP). Response s of BW4 followed the same pattern as that for the selected trait with the response about five times greater during the first 18 than the la st 18 generations of selection in Line HWS and less than two times gre ater in Line LWS. For BW24 and BW38, correlated responses were greater for LWS than for HWS females without feed restriction, suggesting cha nges in growth curves after selection age. Although AFE was delayed in both lines, the delay was greater in Line LWS (some individuals of wh ich were anorexic) than in Line HWS and greater in the second half tha n the first half of the experiment. For pullets that commenced lay, HD P declined slightly in both Lines. Correlations between BW at 4, 8, 24 , and 38 wk of age were moderate to high and positive in both lines. W hen feed intake was restricted in Line HWS, however, there were no cor relations of BW4 or BW8 with BW24 or BW38. Correlations between AFE an d BW at all ages were negative in Line LWS. In Line HWS there were neg ative correlations of AFE with BW24 and with BW38. Relaxed lines, esta blished periodically during the experiment, were satisfactory monitors of environmental influences for primary and correlated traits.