Group records corrected for mortality to estimate breeding values for production traits in laying hens

Records of a White Leghorn Line from three generations were used to evaluate the genetic parameters (heritabilities and breeding values) for production traits in laying hens based on individual and group mean records, taking into account mortality in the data structure. Three different data structures of group mean records, which were Hen Housed Production (HHP), Hen Housed Production corrected for mortality (HHPc) and Survivor Hen Production (SHP) were analysed. The program VCE 5.0 (Kovac et al. 2002) based on the REML method and onetrait sire and two-trait animal-sire models were used to estimate the (co-)variance components of egg productions for individual and group mean records. To account for different relationships in group cages for HHP, HHPc and SHP, a model with heterogeneous residual variances was used. Breeding values of animals from individual records were also estimated using single trait animal models, and breeding values of sires from group mean records were estimated using single trait sire models with heterogeneous residual variances. Spearman rank correlations were used to compare the sire breeding values. As expected the heritabilities for production traits of laying hens estimated based on SHP (0.09-0.37) were higher than those estimated based on HHP (0.040.27) and HHPc (0.08-0.28). The rank correlations between breeding values of all sires estimated based on individual records and those from group cage records estimated with single trait model separately showed lower estimations than those estimated with two-trait animal-sire models simultaneously. Single trait model resulted rank correlations between breeding values for SHP of individual record with HHP, HHPc and SHP of group mean records between 0.21 0.65; 0,37 0,67; 0.30 0.67, respectively. Those for two-trait animal-sire models were 0.89 0.96; 0.96 0.99; 0.93 0.96, respectively. Based on this study, it seems HHPc is a practical approach to optimize the utilization of production traits of laying hens data from group cages for estimating breeding values for egg production.