Validating the breeding value for maternal preweaning gain in beef cattle with measured milk production

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The objective of this research was to validate the maternal breeding value for preweaning gain as a predictor of genetic differences in milk production. Phenotypic variation in preweaning gain and in milk production measured by the weigh-suckle-weigh method was partitioned into genetic and non-genetic components. Data were from the Line 1 Hereford cattle maintained by USDA-ARS at Miles City, Montana, USA. Data collected through 2005 included 6835 and 692 observations of preweaning gain and milk production from 2172 and 403 dams and cows since 1935 and 1994, respectively. Data were analyzed using a Gibbs sampler for multiple-trait animal models. Results are reported as mean ± SD derived from the posterior distribution of parameter estimates. Phenotypic variances of preweaning gain and milk production were 476.3 kg2 and 8.88 kg2, respectively. Heritability estimates for direct and maternal preweaning gain, and milk production were 0.13 ± 0.03, 0.25 ± 0.04, and 0.25 ± 0.06, respectively. Estimates of genetic and phenotypic correlations between preweaning gain and milk production were 0.80 ± 0.08 and 0.37± 0.04, respectively. The difference between phenotypic and genetic correlations may provide insight into confidence of breeders in genetic evaluation of maternal preweaning gain. Breeding value for maternal preweaning gain was highly predictive of breeding value for milk production. Selection based on the maternal breeding value for preweaning gain may be nearly as effective in changing milk production as direct selection. Keywords: Genetic correlation;growth; heritability South African Journal of Animal Science Vol. 36 (5) 2006: pp.1-5