J. Anim Sci.
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J. Anim Sci. 1985. 60:1133-1141.
© 1985 American Society of Animal Science
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Selection for Weaning Weight and Postweaning Gain in Hereford Cattle. I. Population Structure and Selection Applied1

R. Irgang2, E. U. Dillard3, M. W. Tess3 and O. W. Robison3

North Carolina State University, Raleigh 27695-7621

Abstract

Single trait selection was practiced in three lines of Hereford cattle derived from a common base population. Selection was practiced on males only within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Females were culled on the basis of age or reproductive failure. Progeny of selected bulls were produced in two herds from 1970 through 1981. The data consisted of records on 2,467 progeny of 125 sires and 922 dams. Generations of selection to produce the 1981 calf crop were 1.96, 1.85 and 1.80 for WWL, PGL and CTL, respectively. For calves born in 1981, mean cumulative selection differentials (CSD) were 54.5 kg in WWL and 37.8 kg in PGL. Corresponding values in standard deviation units (SDU) were 2.31 and 1.68, respectively. Secondary selection differentials were 25 to 40% as large as selection differentials for the primary traits. Unintentional selection in the CTL in 1981 was 16.2 kg or .68 SDU for WW and .2 kg or .01 SDU for PG, respectively. Regressions of CSD on year were 4.1 kg or .17 SDU in WWL and 3.2 kg or .14 SDU in PGL. Realized selection differentials were approximately 88% of the potential selection differentials in both lines. Inbreeding coefficients of dam and calves in 1981 were 2.0 and 3.5% in WWL, 2.1 and 3.5% in PGL and 2.9 and 5.8% in CTL.

Footnotes

1 Paper No. 9416 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh 27695-7601.

2 Present address: Centro Nacional de Pesquisa de Suinos e Aves, EMBRAPA, C.P. D-3, 89.700-Concordia, Santa Catarina, Brazil.

3 Dept. of Anim. Sci.






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Copyright © 1985 by the American Society of Animal Science.