Mixed model studies on inheritance of reproductive traits in laying hens - a Bayesian approach

Segregation analyses performed for many livestock species indicate a mixed inheritance model of reproductive traits. Additionally, depending on the population, a given trait can be determined by a number of genes with large effects. Genetic backgrounds of hatch-ability and fertility in poultry are still not known sufficiently. The objectives of this study are to verify the hypothesis on segregation of single genes (1 vs. 2) affecting fertility and hatchability and to estimate a heritability of these traits. Records from 2,040 and 2,015 dams from full-pedigreed strains of Rhode Island Red (R33) and New Hampshire (N88) from a pedigree farm were analyzed. The percentage of fertilized eggs and the percentage of the eggs hatched of fertilized eggs were registered for dams only. Fertility was checked by candling on the eighth day of incubation. To obtain a binomial phenotypic scale, 10 eggs per dam were included into the analysis. Animal single-trait threshold models were used for the analysis of data. The first model included the effects of 2 single genes, 2 fixed effects of year and season, additive polygenic effects, and permanent environmental effects. In the second model, only 1 single gene effect was included. Additionally, the analysis based on the polygenic threshold model was also performed. The Gibbs sampling procedure was used. The significance of single gene effects was verified by highest posterior density regions. The obtained results clearly gave evidence for the segregation of 1 major gene for hatchability in strain R33. Furthermore, the mixed inheritance model can also be suggested for fertility in this strain. After the analysis, the polygenic heritabilities were very low (<0.11), whereas major polygenic heritability ranged from 0.05 to 0.12.