A major part of the growth performance in birds is the result of the combined effects of genes, including the general and specific combining ability that requires the design of an optimal mating system. The aim of this study was to fit the best model for each body weight trait from hatch to 45 days and the estimation of the variance components and the genetic parameters for the body weight traits of a crossbred population. This crossbred population was created by 4 strains of Japanese quail, including the Italian Speckled (A), Tuxedo (B), Pharaoh (C), A&M Texas (D), and the body weights of the different combinations were analyzed by 24 models including the direct genetic effect, the non-additive genetic effects including dominance and epistatic effects, the maternal permanent environmental and maternal genetic effects. The selection of the best fit model of each trait was performed based on the deviance information criteria. The variance components were estimated using a single-trait animal model analyzed with Gibbs sampling. At the early stage of bird growth, maternal genetic and maternal permanent environmental effects had a considerable contribution to the best model, but the contribution of these effects reduced with an increase in the bird's age and the additive variance contribution increased. Adding non-additive genetic effects (dominance and epistasis) to the models significantly reduced the variance of the error and the additive genetic variance estimated with high accuracy. The estimated heritability of body weight traits for the body weights of hatch, 5, 10, 15, 20, 25, 30, 35, 40, and 45 d were 0.316, 0.170, 0.251, 0.153, 0.132, 0.164, 0.290, 0.425, 0.476, and 0.362, respectively. The ratio of maternal genetic and maternal permanent environmental was considerable especially on early age body weight but the ratio of dominance and epistatic variances on each of the body weight traits was less than 4.5% of the total variance, but led to a more accurate estimates of the direct additive genetic.

The main part of growth performance in birds is as a result of gene combination effects, which their changes require an optimal mating system in order to use general and specific gene combination ability. The purpose of the present study was to evaluate the growth patterns of four strains combination Japanese quail in a partial di-allele cross. For this purpose, four strains of Italian Speckled (A), Tuxedo (B), Pharaoh (C), A&M Texas (D) were used in a partial diallele cross design to produce different gene combinations during four generations. Four functions including Gomperts, Richards, Logistic and Weibull were fitted for body weights records of different combinations. The best function for each combination was selected by goodness of fit criteria's. Then, function parameters and growth patterns of the best function were compared between combinations. The results of goodness of fit criteria's showed that the Gompertz function was the best one for binary combinations of AB, BA, CD, DC and reciprocal combination of ABCD-DCBA, DCBA-ABCD, while Weibul function was found to be the best function for quadrille combinations of ABCD, DCBA for describing growth curve. The effects of year and month of hatching on all growth patterns were significant (P<0.05). Also, the combination effect on initial weight, final weight, age and weight at inflection point and, oneday weight was significant (P<0.05). The effect of sex on curve growth parameters was not significant (P>0.05) except for 45-days weight. The DC combination had the highest initial and final weight, age and weight at inflection point compared to other combinations. The quadrille combinations, especially DCBA had the highest final weight, 45-days weight and, 45-days growth rate, but the lowest puberty index. Also, age and weight at inflection point in DCBA combination were at moderate level among combinations and showed better performance compared to other crosses indicating of the most heterosis in this combination.