Genetic parameters for preweaning and growth traits estimated using different statistical models

The objective was to compare estimates of genetic parameters resulting from different analytical models and estimates of breeding values for birth weight (BWT, n = 4155), 205-d weaning weight (WWT, n = 3884) and 365-d yearling weight (YWT, n = 3476). Data consisted of records on Line 1 Hereford cattle selected for postweaning growth from 1934 to 1989 at ARS-USDA Miles City, MT. Twelve models were compared: Model 1 included fixed effects of year, sex, age of dam, covariates for birth day, inbreeding coefficient of animal and inbreeding coefficient of the dam, and random additive direct animal genetic and residual effects. Model 2 was the same as Model 1 but ignored inbreeding. Model 3 was the same as Model 1 and also included random additive maternal genetic effects with covariance between direct and maternal genetic effects, and permanent maternal environmental effects. Model 4 was the same as Model 3 but ignored inbreeding. Model 5 was the same as Model 1 but with a random sire effect instead of animal genetic effect. Model 6 was the same as Model 5 but ignored inbreeding. Model 7 was also a sire model, but considered relationships among males. Model 8 was a sire model, assuming sires to be unrelated, but with dam effects as uncorrelated random effects to account for maternal genetic and permanent environmental effects. Model 9 was a sire and a dam model, but with relationships to account for direct and maternal genetic effects; dam effects also were used as uncorrelated random effects to account for maternal permanent environmental effects. Model 10 was a sire model with maternal grandsire and dam effects all as uncorrelated random effects. Model 11 was a sire and a maternal grandsire model with dam as an uncorrelated random effect but with sires and maternal grandsires assumed to be related using the male relationships and full relationships (Model 12). Estimates of variance components as proportions of total variance, and ranking on estimates of breeding values were the same whether or not inbreeding coefficients for animal and dam were included in the statistical models. For birth, weaning, and yearling weights the full animal model (Model 3) was needed to estimate variances and covariance for direct, maternal genetic and permanent environmental effects although the sire and dam model with relationships gave similar estimates. Heritability estimates of direct effects were smallest from sire and sire-maternal grand sire models