Genetic and phenotypic parameters for monthly egg production in White Leghorn hens

This article reports genetic and phenotypic parameters of monthly egg produ ction and the influence of Box-Cox transformation on the parameters from a population of White Leghorns, selected for feed efficiency. A total of 6450 daughters of 180 sires and 1335 darns were analysed by restricted maximum likelihood (REML) using a multivariate animal model. The traits considered were monthly egg productions, cumulative production of the first 5 months ( S5), cumulative production of first 10 months (S10), and survivor egg produ ction in the first cycle (S12). Two sets of data were analysed: the origina l data and with the Box-Cox method transformed data. The results indicated that there were no great differences in the estimates between untransformed and transformed data. The estimates of heritability for monthly egg produc tion were high for the first period, decreased to reach the lowest during p eak production, and Increased to the end of lay. The estimates of heritabil ity for cumulative records were generally higher than monthly records. Gene tic and phenotypic correlations among monthly egg production totals were ge nerally high for contiguous periods and then decreased as the interval betw een months increased. The highest genetic correlation between monthly recor ds and S5 was for the second month of production, whereas the correlations between monthly production totals and S10 and S12 reached their peak at the sixth and eighth months of production, respectively.