Estimates of Genetic and Phenotypic Correlations Between Monthly and Cumulative Egg Productions in a Commercial Broiler Female Line

The purpose of this study was to estimate genetic and phenotypic correlations between monthly and cumulative egg productions in a commercial broiler line. Egg productions of 16483 hens from 1198 sires and 4564 dams were used in the analysis. The period of data collection was from 24 to 55 weeks of age. From the weekly productions, 8 monthly records on 28-day basis and a cumulative egg production were created. A multi-trait animal model using Restricted Maximum Likelihood (REML) was used to estimate (co)variance components of egg records. The estimates of heritability for monthly records ranged from 0.076 (M8) to 0.424 (M1). The first month showed the highest heritability among all periods. Also, the heritability of 0.147 was obtained for cumulative egg production. Genetic correlations between cumulative egg numbers and monthly records varied from 0.651 (with first month) to 0.946 (with sixth month). The corresponding estimates for phenotypic correlations were generally lower than the genetic correlations. However, the pattern of variations was almost similar. With considering age at sexual maturity as a covariate in the model, the genetic and phenotypic correlations between the first month and cumulative egg production decreased by about 64.06% (from 0.651 to 0.234) and 50.61% (from 0.413 to 0.204), respectively. The results of this study showed that improvement of cumulative egg number is feasible through selection according to each monthly record after second month.