Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/1999
Publication Date: N/A
Citation: Interpretive Summary: Selection is an effective means for changing characteristics of populations. Basing selection on easily and routinely measured growth traits, while achieving the intended direct responses, may not favorably impact all components of production efficiency. The correlated increases in fatness resulting from selection on increased yearling weight and reduced birth weight provide one such example. In addition, not all consequences of selection may be easily anticipated from pre-existing parameter estimates as illustrated by the increase in breeding value for gestation length of sires selected for increased yearling weight and reduced birth weight. Selection for low birth weight and high yearling weight was thought to improve production efficiency without changing body composition. This experiment used semen from bulls of different generations to establish genetic trends in components of production efficiency. Growth, feed intake, and carcass attributes expressed from conception to retail product were evaluated.
Technical Abstract: Breeding values of sires resulting from selection either for reduced birth weight and increased yearling weight (YB) or for increased yearling weight alone (YW) were compared with each other and with sires representative of the population before selection began (BS) using progeny testing. Twenty-nine sires produced 525 progeny that were evaluated through weaning. After weaning 225 steer progeny were individually fed, slaughtered, and carcass data collected. Data were analyzed using restricted maximum likelihood procedures for multiple traits to estimate breeding values for traits measured on the top-cross progeny while simultaneously accounting for selection of the sires. Results of the progeny test substantiate within line results for traits upon which sires were selected. Breeding value for gestation length was greater in YB sires than in YW sires which were unchanged relative to BS sires. Breeding values for growth rate and feed intake of both YB and YW sires were greater than BS sires. Genetic propensity for fat deposition tended to greater in YB sire and less in YW sires relative to BS sires, although YB and YW sires had similar breeding values for marbling score. Selection based on easily and routinely measured growth traits, while achieving the intended direct responses, may not favorably impact all components of production efficiency. Further, divergence of selection lines may not be easily anticipated from pre-existing parameter estimates, particularly when selection is based on more than one trait.