The objective of the current study was to evaluate a multi-trait selection program based on aggregated breeding values using an animal model Best Linear Unbiased Prediction (BLUP) in Japanese quail. The estimated genetic gain was compared by both mixed model and least squares methods. Data of 1,682 female Japanese quails were collected through four consecutive generations to estimate genetic gain, depending on aggregated breeding values, for age at first egg (AFE), body weight at sexual maturity (BW_SM), and days needed to produce the first ten eggs (DN₁₀). Estimates of cumulative selection response were favorable for all the studied traits and significant for AFE (–3.03) and BW_SM (10.38), but not significant for DN₁₀ (–0.15). Estimates of direct heritability were moderate for AFE (0.21) and BW_SM (0.25) but low for DN₁₀ (0.08), while estimates of maternal heritability were moderate for AFE (0.19) but low for BW_SM (0.04) and DN₁₀ (0.01). High (0.45 to 0.56) genetic and low (–0.01 to –0.18) phenotypic correlations were observed among the studied traits. Negative (–0.23 to –0.95) correlations between additive genetic and maternal genetic effects were observed for all traits. Genetic trends were –0.76 (P = 0.031), 2.54 (P = 0.037), and –0.06 (P = 0.052) with calculated product-moment correlations between breeding values, estimated by BLUP and phenotypic selection methods, of 0.78 (P = 0.002), 0.77 (P = 0.004), and 0.61 (P = 0.007) for AFE, BW_SM, and DN₁₀, respectively. Aggregated breeding value estimation based on animal model BLUP could be an effective method of constructing a selection program to achieve a favorable selection response in egg production traits in Japanese quail.

The main objectives of this study were to detect the most appropriate random regression model (RRM) to fit the data of monthly egg production in 2 lines (selected and control) of Japanese quail and to test the consistency of different criteria of model choice. Data from 1,200 female Japanese quails for the first 5 months of egg production from 4 consecutive generations of an egg line selected for egg production in the first month (EP1) was analyzed. Eight RRMs with different orders of Legendre polynomials were compared to determine the proper model for analysis. All criteria of model choice suggested that the adequate model included the second-order Legendre polynomials for fixed effects, and the third-order for additive genetic effects and permanent environmental effects. Predictive ability of the best model was the highest among all models (ρ = 0.987). According to the best model fitted to the data, estimates of heritability were relatively low to moderate (0.10 to 0.17) showed a descending pattern from the first to the fifth month of production. A similar pattern was observed for permanent environmental effects with greater estimates in the first (0.36) and second (0.23) months of production than heritability estimates. Genetic correlations between separate production periods were higher (0.18 to 0.93) than their phenotypic counterparts (0.15 to 0.87). The superiority of the selected line over the control was observed through significant (P < 0.05) linear contrast estimates. Significant (P < 0.05) estimates of covariate effect (age at sexual maturity) showed a decreased pattern with greater impact on egg production in earlier ages (first and second months) than later ones. A methodology based on random regression animal models can be recommended for genetic evaluation of egg production in Japanese quail.

Estimation of correlated response to selection in female line of Japanese quail after a short-term selection experiment was conducted. The total number of 547 female (275 selected and 272 control) Japanese quail included in the selection experiment of selection depended on aggregate breeding values based on animal model Best Linear Unbiased Prediction. Correlated selection response estimates were favourable for all the studied traits and significant (–0.38, –9.89, –12.86, –16.64, –5.08 and –8.24) for first egg weight (FEW), age at the first 10 eggs (AGE10), age at first 30 eggs (AGE30), age at first 60 eggs (AGE60), days needed to produce the first 30 eggs (DN30) and the first 60 eggs (DN60), respectively. Estimates of heritability were moderate for egg mass for the first 10 eggs (EM10), the first 30 eggs (EM30), the first 60 eggs (EM60), AGE10 and AGE30 (0.17–0.30), but low for AGE60, DN30 and DN60 (0.01–0.10). Genetic correlations between the selection criteria traits (AFE, BWSM and DN10) and the studied egg production traits were positive and ranged from 0.25 to 0.97, 0.24 to 0.95 and 0.06 to 0.98 for AFE, BWSM and DN10, respectively, whereas phenotypic correlations ranged from 0.12 to 0.89, 0.01 to 0.34 and 0.06 to 0.87 for the same traits. The favourable genetic response obtained for egg traits could be an indicator for improving egg production performance in Japanese quail.

The current study investigated the influence of selection for body weight (BW) on growth curve parameters in two lines of Japanese quail through a mixed model approach. Live BWs of 1400 Japanese quail were recorded at 3-day intervals from hatching to 42 days of age. Birds were distributed equally across lines (selected and control) and sexes (male and female). The asymptotic weight parameter (β₀) values were always higher in Gompertz than Richards models in both lines. The values ofβ₀were higher in the selected than control lines and in females than males across models. Differences were found in the inflection point for age and weight across lines and sexes. Values of the growth rate parameter (β₂) ranged from 0.06 to 0.10 in both models, favouring males over females in both lines. Lower weights at the inflection point of both models were observed in the control line. Determination coefficient (R²) of both models in different genetic groups and sexes was similar. Mean square error (MSE) values of the Gompertz model were lower for females in selectedv.control lines. In contrast, MSE values of the Richards model were lower for selected malesv.control males. According to the criteria of choice (highestR²and lowest MSE, Akaike information criterion and Bayesian information criterion), the Richards model was considered the best fitting model for the growth data of males, while the Gompertz model was the best for growth data of female quails in both lines.

This study aimed to evaluate the impact of partial-record egg production selection on egg production performance, serum biochemical constituents, and egg quality traits in Dokki-4 laying hens. A selection experiment was conducted over four generations involving 2,880 hens distributed across three experimental lines: high egg number line (SHEN₉₀), heavy egg weight line (SHEW₉₀), and a random-bred control line (RBCL). Selection criteria were based on performance during the first 90 days of production. Line effects were highly significant for all egg production traits, serum calcium concentrations, yolk cholesterol levels, and most egg quality traits. The SHEN₉₀ line showed superior egg number, annual egg mass production performance, and exhibited favorable metabolic profiles with reduced serum cholesterol and triglycerides. The SHEW₉₀ line achieved significantly heavier egg weights and improved shell quality traits compared to other lines. Genetic gain estimates revealed significant improvements in economically important traits. The SHEN₉₀ line showed favorable genetic gains for EN₉₀, EM₉₀, EM₃₆₅, and favorable reductions in serum cholesterol, triglycerides, and yolk cholesterol. The SHEW₉₀ line exhibited significant positive genetic gains in EW₉₀, EM₉₀, EM₃₆₅, and favorable yolk weight and yolk index percentages. Heritability estimates were moderate for selection criteria (EN₉₀: 0.22; EW₉₀: 0.17) and ranged from 0.09 to 0.31 for correlated traits. Genetic correlations revealed strong positive relationships between EN₉₀ and egg mass traits. EW₉₀ showed positive correlations with most external quality parameters. Selection for partial-record egg production represents an effective breeding strategy for simultaneously improving multiple economically important traits in Dokki-4 laying hens.