Comparison between two methods for estimating variance components for production traits in laying hens

The objective of the study was to compare variance components estimated with a sire model and HENDERSON III with an animal model and REML for egg production and other production traits in laying hens. Special attention was paid on the estimation of covariances between different parts (periods) of full year egg production. Variance components were estimated from performance data of 2618 pure line Rhode Island Red and 6355 White Rock laying hens. Heritability estimates based on REML in different periods for egg production feed intake and body weight have been higher than for HENDERSON III. For different egg weights REML showed more uniform estimates and no significant increase compared to HENDERSON III. Correlations between egg production in different periods can be outside of the parameter range when estimated with HENDERSON III. If the complex relationships are utilized parameters from different periods are more consistent. For breeding value estimation egg production in period 1, period 2 to 6 and period 7 to 10 should be used in a multiple trait animal model in combination with other production and quality traits. Production rate in period 1 has to be used as a separate trait, because it is high correlated with age at sexual maturity. Heritability for period 1 is higher than in other periods and correlations to other periods differ clearly from later stages of production.