COMPARISON BETWEEN 2 METHODS FOR ESTIMATI NG VARIANCE-COMPONENTS FOR PRODUCTION TRAITS IN LAYING HENS

The objective of the study was to compare variance components estimate d with a sire model and HENDERSON III with an animal model and REML fo r egg production and other production traits in laying hens. Special a ttention was paid on the estimation of covariances between different p arts (periods) of full year egg production. Variance components were e stimated from performance data of 2618 pure line Rhode Island Red and 6355 White Rock laying hens. Heritability estimates based on REML in d ifferent periods for egg production feed intake and body weight have b een higher than for HENDERSON III. For different egg weights REML show ed more uniform estimates and no significant increase compared to HEND ERSON III. Correlations between egg production in different periods ca n be outside of the parameter range when estimated with HENDERSON III. If the complex relationships are utilized parameters from different p eriods are more consistent. For breeding value estimation egg producti on in period 1, period 2 to 6 and period 7 to 10 should be used in a m ultiple trait animal model in combination with other production and qu ality traits. Production rate in period 1 has to be used as a separate trait, because it is high correlated with age at sexual maturity. Her itability for period 1 is higher than in other periods and correlation s to other periods differ clearly from later stages of production.