Genetic and Environmental Parameters Analysis of Weekly Egg Weights in Wild and White Japanese Quails

The aim of the current study was to estimate the genetic and environmental parameters for weekly egg weights using a random regression model in wild and white Japanese quails. The base population included 300 wild and white Japanese quails, with a mating ratio of 1:2 (one male with two females). Four mating groups including pure and cross-breeding methods, were considered to produce the next generation. Eggs were collected and numbered based on their sire and dam. At the fifth week of age, 508 female quails were transferred to the laying cages. The data on egg weight was recorded from the seventh to fifteenth week of age. Nine random regression models were analyzed to determine the best orders of Legendre polynomials. The model with first and second-order Legendre polynomials for additive genetic and permanent environmental effects, respectively, indicated the lowest AIC value and was chosen as the appropriate model. The heritability estimates and the ratios of the permanent environment to the phenotypic variance of weekly egg weights ranged from 0.09 to 0.35 and from 0.08 to 0.51, respectively. The effect of permanent environmental factors on the average weight of laid eggs decreased with increasing laying weeks, followed by an increase in the additive genetic effect on the occurrence of this trait. The estimates of genetic and phenotypic correlations between weekly egg weights varied from 0.59 to 0.98 and from 0.21 to 0.51, respectively. As a result, because of higher heritability estimates for later ages, selection to improve weekly egg weight is better performed based on at least the fifth week of the laying period onward. In conclusion, due to high positive genetic correlations among weekly egg weights, the selection basis of each weekly part record can lead to improving the consecutive weekly egg weights.