Estimates of genetic parameters for monthly egg production traits in a commercial broiler female line

摘要

In this study, genetic parameters for monthly records of egg production, collected from weeks 24 to 55 on 16,830 hens during nine generations from a pedigreed commercial broiler female line, were estimated with single-trait, multiple-trait and repeated records animal models, using restricted maximum likelihood procedures. With and without age at sexual maturity as a covariate, two models were fitted to the data for each analysis. From the weekly productions, eight monthly records on a 28-day basis were created. The estimate of heritability from single-trait analysis for the first month’s record was relatively high (0.428), decreased to 0.150 and 0.092 in the second and third months, respectively, and then, with minor fluctuations, remained constant. Age at sexual maturity had a substantial influence only on heritability of the first month (0.192) and, to some extent, of the second month (0.103). Estimates of heritability and repeatability decreased from 0.067 and 0.379 to 0.029 and 0.251, respectively, owing to age at sexual maturity. Genetic correlations were generally positive, being relatively high to very high between adjacent monthly records, ranging from 0.725 (between the first and second month) to 0.986 (between the fourth and fifth month). These estimates between monthly records decreased as the time interval of the ages increased. The effect of age at sexual maturity on reduction of heritability of the first month’s record and of its genetic correlations with all other monthly records suggests that it is essentially necessary to be included in the model or that the analysis is carried out without the first month’s record.