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Genetic Parameters and Consequences of Selection for Growth Traits in a Beef Herd Selected for Yearling Weight^1,2,

Purdue University, West Lafayette, IN 47907

Abstract

Data from 2,576 calves produced in a single Angus herd were analyzed to obtain estimates of heritability, genetic and phenotypic correlations, and cow performance repeatabilities. Traits analyzed were birth weight (BWT), 205-d weight (WWT), 365-d weight (YWT), postweaning gain (PWG) and gain from birth to 365 d (PBG) in the male and female data sets. Heritabilities and correlations were higher in the male data set than in the female set. Heritabilities estimated by intraclass correlation from the male and female data sets, respectively, were .51 and .41 for BWT; .30 and .21 for WWT; .36 and .18 for YWT; .38 and .27 for PWG; and .34 and .18 for PBG. Genetic correlations were consistently smaller in female data than in male data. Genetic correlations were consistently smaller in female data than in male data. Genetic correlations ranged from .37 between WWT and PWG to .99 between YWT and PBG in the male data, and from .10 between BWT and PWG to .99 between YWT and PBG in the female data. Repeatibilities of calf weights and gains as traits of the dam were estimated by dam components of variance. The estimated repeatibilities for male and female data sets, respectively, were .26 and .29 for BWT; .43 and .28 for WWT; .21 and .48 for YWT; .05 and .75 for PWG; and .20 and .49 for PBG. Expected changes in YWT were 15.18 or 14.67 kg per generation, respectively, when either YWT or PBG was the sole criterion of selection. Genetic change in YWT was reduced by 31 to 47% when using a selection index that was constructed to produce zero change in birth weight.

¹ Journal Paper No. 10,637 of the Purdue Agr. Exp. Sta. A contribution from the Dept. of Anim. Sci.

² Data were derived from the Purdue contributing project to the NC-1 regional project entitled "Improvement of Beef Cattle Through Breeding Methods."

³ Supported by a fellowship sponsored by the Instituto Nacional Investigaciones Agrarias of Spain and The World Bank.

⁴ Present address: INIA-CRIDA 06, Dept. of Genet., Apartado 8111, Madrid, Spain.