02585nam a2200385 a 450000100080000000500110000800800410001910000150006024501090007526000510018430000100023550000200024552016420026565000160190765000110192365000090193465000190194365000180196265000160198065000120199665000090200865000180201765000120203565000100204765000090205765000220206665000140208865000140210265300150211665300080213165300200213965300110215965300150217065300140218513232242014-01-15       1984    bl uuuu  m   00u1 u    #d1 aIRGANG, R.  aDirect and correlated responses to selection for weaning weight and postweaning gain in Hereford cattle.  aRaleigh: North Carolina State Universityc1984  a165p.  aTese Doutorado.  aSingle trait selection was practiced in three lines of Hereford cattle derived from a common base population. Bulls were selected within sire families for increased weaning weight (WW) in line WWL, increased postweaning gain (PG) in line PGL and ramdomly selected in the control line (CTL). The data consist of 2,467 progeny produced from 1967 to 1981 by 125 sires and 922 dams. After 3 years of stablishing the foundation population, 12 years of continuous selection resulted in slightly less than two generations of selection of selection and in low inbreeding coefficients. Direct selection applied to either WW or PG improved both traits. However, selection for PG increased both PG and WW faster than selection for WW. Selection for WW and for PG increased milk production, preweaning daily gain, yearling weight and feed intake. Correlated responses in these traits were larger in PGL than in WWL. Selection for either WW or PG also increased the amount of fatness in bulls in feedlot. However, it did not result in any or PG also increased the amount of fatness in bulls in feedlot. However, it did not result in any significant change in feed efficiency. Increased birth weight was observed from PG selection but not from WW selection. Realized heritabilities and regression coefficients of correlated responses on cumulative selection differentials, estimated from "quasi-replicates" generated by grouping individual descendents from sires utilized in different years of the foundation population, indicated that genetic drift affected responses to selection and suggest that replication of selection experiments is necessary...  abeef cattle  acattle  amilk  aweaning weight  aAlimentação  aCrescimento  aDesmama  aGado  aGado de Corte  aGordura  aLeite  aPeso  aProdução Animal  aSeleção  aZootecnia  aBeefcattle  aFat  aFeed efficiency  aGrowth  aProduction  aSelection