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Estimating variances due sire x herd effects requires a large number of sires to be represented in multiple herds, otherwise too much variation between animals is 'picked up' as variance due to sire x herd effects, and heritability estimates are biased downwards. Such bias can be avoided by using only records for progeny of multiple-herd use sires to estimate the additive genetic variance. Estimates of variance components and genetic parameters from analyses of weights of Hereford cattle are presented for herds with high, medium and low proportions of sires used across multiple herds. Results from analyses estimating separate genetic variances for progeny of single and multiple herd sires, estimating a joint genetic variance for all animals, and ignoring sire x herd effects are compared. |
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