Direct and Correlated Responses to Selection for Increased Weaning or Yearling Weight in Angus Cattle. II. Evaluation of Response2

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Abstract
Three lines of Angus cattle were selected for individual weaning weight (WWL), individual yearling weight (YWL) or a combination of individual and progeny weaning weights (PTL) from 1965 to 1979. Also, a contemporary Angus control line (CL) was maintained to monitor yearly environmental changes. Each line consisted of 50 cows with two buUs and 10 heifers being selected on line criteria within each line each year. Selected bulls were used for 2 yr. Performance data through yearling age were collected on 694, 691, 666 and 698 calves in the WWL, YWL, PTL and CL, respectively. Traits analyzed were birth weight (BW), preweaning daily gain (WDG), weaning weight (WW), weaning conformation grade (WG), weaning condition score (WC), weaning to yearling daily gain (YDG), yearling weight (YW), yearling conformation grade (YG) and yearling condition score (YC). Averaged over two methods, estimated genetic responses in Standard measure/generanon in WWL, YWL and PTL, respectively, were: BW, .24, .47, .42; WDG, .25, .23, .46; WW, .28, .30, .51;WG, .10, .08, .18; WC, .14, −.03, .08; YDG, .12, .36, .16; YW, .26, .44, .41; YG, .12, .21, .10; and YC, .00, .03, −.04. Realized heritabilities were .30 for WW and .38 for YW, and the realized genetic correlarion between WW and YW was .79. The final group of bulls selected on line criteria (four bulls/line born in 1978) were randomly mated to a group of Angus cows to produce 201 calves in 1980. In general, growth and carcass performance of progeny from selection line sires exceeded (P<.05) that of progeny from CL sires. Mature cows from the WWL produced .77 kg/d (P<.10) more milk than cows from the CL. Milk yield of YWL cows was intermediate and not significantly different from either WWL or CL cows. Copyright © 1986. American Society of Animal Science. Copyright 1986 by American Society of Animal Science

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