Genetic Evaluation of Egg Production and Egg Quality Attributes in Japanese Quails through Partial Periods

Quail production has turn into an eminent niche in the Indian poultry market. Introduction of projects that can genetically improve birds for efficient and effective productivity are essential. An estimate of genetic parameters is highly necessary for genetic improvement program of important economic traits. Egg production efficiency is typically measured through age and body weight at sexual maturity, egg number and egg weight during certain production periods, etc. Increased egg weight and number of eggs are the primary purpose of the laying bird breeding programmes. A poultry breeder’s eventual goal is to optimize the bird’s overall genetic economic value by multi trait selection by exploring the greater number of traits at a time (Narinc et al., 2015). Egg production in layers varies over the entire production cycle. Therefore, selection can be framed in terms of partial production periods (Poggenpoel et al., 1996). This procedure enhances the overall production of eggs and may consequently results in greater genetic gain with decrease in the generation interval at each selection cycle (Lopes, 2005; Karami et al., 2017).
        
Beside egg production performance, egg quality (both external and internal traits) is also important for human consumption and for hatcheries. From the breeder’s perspective the relationship between egg production and quality is utmost important. Numerous studies revealed that egg quality can be altered through selection for economic traits (Silversides and Scott, 2001). There are many detailed studies on the evaluation of genetic parameters for egg production and egg quality traits mostly for chicken layers in the literature (Saatci et al., 2006; Hidalgo et al., 2011). However, a paucity of information on genetic and phenotypic correlations between production performance and egg quality traits exists in Japanese quail. The aim of present study was to estimate phenotypic and genetic correlations to improve performance and egg quality traits in Japanese quail reared with one to one sire and dam pedigree data, at the Central Avian Research Institute (CARI), Izatnagar, Bareilly, UP, India.

The official approval number of Institute Animal Ethical Committee (IAEC) was 452/01/ab/CPCSEA. In present investigation, data recording was carried out from the Japanese quail population at experimental quail farm, CARI during 2019-2020. The pedigree population were descended from 180 sires and 180 dams of each variety (CARI-UJJAWAL; CARI-SUNEHERI and CARI-BROWN) of domesticated Japanese quails. Birds were randomly selected from the base populations to develop first generation of experimental population. For correct pedigree recognition, adult matting pairs were housed in individual cages (L*H = 25 * 15 cm) and performed mating. Pedigreed and fertile eggs (breeder flock age- 8 to 11 weeks) were obtained twice daily from each of the three varieties. The collected egg was numbered so a complete pedigree was available for each egg according to its sire and dam. Collected eggs were successfully hatched out using pedigree boxes. The hatched chicks were wing banded and the pedigree details were recorded.
        
For egg production evaluation, 200 birds which were progeny of 40 sires and 40 dams selected from each variety. They were transferred to individual laying cages after the 5^th week of age for recording of egg production traits. The females of each variety were transferred to individual laying cages to observe age at sexual maturity (ASM), measured from the date of hatch till the pullets start laying their first egg. Part-time egg production of each bird was recorded bi-weekly at 8th to 18th week of age. For egg quality traits estimation 360 eggs were taken for assessment at 12^th week of age which was descended from same 40 sire dam progenies. The parameters were discussed below.
 
1. Egg weight (EW): The egg weight was individually determined with weighing balance (g).
2. Shape index (SI): The shape index was computed using the following formula (Schultz, 1953).          
3. Specific gravity (SG): It was measured by the floatation method in which a series of sodium chloride solution (Voisey and Hamilton, 1977).
4. Shell thickness (ST): Shell thickness was estimated on samples taken at three sites; at equator, from the blunt and pointed end of each of sample eggs using micrometer gauge.
5. Surface area (SA): Egg surface area (cm²) was accounted using the formula (Polat, 2007).  
6. Volume (V): Considered from the following equation (Mohsenin, 1970).
                              
7. Shell percentage (SP): It was computed by using the formula:
              
b) Internal egg quality
 
1. Haugh unit (HU) score calculated using formula (Haugh, 1937).
   
2. Albumen Index (AI): It was calculated as per the formula (Heiman and Carver, 1936).
                      
3. Albumen weight (AW) and yolk weight (YW): It was measured using the electronic weighing balance (g).
4. Yolk index (YI) was evaluated as per the formula (Funk, 1948). 
   
6. Yolk color (YC) was measured using Roche color fan. This consists of a series of 15 colored plastic tabs arranged as a fan corresponding to the range of yolk colors found in eggs.
 
Statistical analysis
 
The least squares mean determination was analysed by JMP, mixed effect model Version 14.0. Variance components were assessed by Wombat (Full sib analysis) mixed model analysis by Restricted Maximum Likelihood (REML) using an animal model. The data were classified in accordance with fixed effects viz. variety of the Japanese quail (CARI-UJJAWAL; CARI-SUNEHERI and CARI-BROWN) and hatch (1^st, 2^nd and 3^rd hatches).
The data available was subjected to the following model as, 
 
Where,
y is a vector of observations, b is a vector of fixed effects with incidence matrix X, a ~N (0, Aσ² a) is vector of direct additive genetic effect with incidence matrices Z1, e ~N (0, Iσ² e) is a vector of random residual effects.

Least-squares means and standard errors by variety and hatch for biweekly egg production traits were revealed in Table 1. The ASM was significantly (p<0.01) affected by varieties and also hatches. Among all varieties, CARI-UJJAWAL matured earlier (45.76 days) followed by CARI-Brown (48.58 days) and followed by CARI-SUNEHERI (51.57 days) matured late. Studies reported a wide range of ASM (42-56 days) in Japanese quail which is in harmony with the present investigation (Devi et al., 2010; Lofti et al., 2012). This may be due to higher selection intensity on increasing body weight in Japanese quail resulted a negative trend in ASM trait (Syed Hussein et al., 1995). In this present study, the third hatch recorded less ASM (46.18 days) followed by 2^nd hatch (49.31 days) and subsequently by 1^st hatch (50.42 days). This significant variation in the hatch effect on ASM indicates that birds from aged dams start their oviposition earlier than the younger ones. Similar observation was presented by Reddish et al., (2003) that second hatch (48 days) exhibited shorter ASM than first hatch (49.7 days).


        
In comparison with other two populations, CARI-UJJAWAL showed the highest mean during the initial laying period. Significant variations between the varieties were seen on egg number up to 8^th week (P<0.01) and at 14^th week (P<0.05). At other week no any significant difference was observed in EN among three quail populations. Such findings are in harmony with Jatoi et al., (2013), who were unable to detect a significant difference (P<0.05) in the eggs production between different chicken strains. However, Hanan, (2010) observed substantial differences in the percentage of egg production at different laying periods Japanese quails. The disparity in strains/variety used could be contributed to variations in the results. Present findings showed that hatch of 8^th to 12^th week traits (P<0.01) had major impact on EN.
        
Least-squares means and standard errors by variety and hatch for egg quality traits were revealed in Table 2. The overall values concerned to EW, SI, SW and average ST were 12.59 g, 78.33%, 1.33 g and 0.21 mm, respectively. The mean egg weight obtained in this study was greater than the 11.28 g and 11.06 g as reported by Sezer (2007), respectively but lesser than Kumari et al., 2016 (13.63 g). This difference could be owing to the result of breed/variety/ strain and environment. The other external qualities such as SW, SI and ST were analogous to the conclusions drawn by Kumari et al., (2016). Among the external qualities EW, SI, SP, SG depicted a significant (p<0.01) variations among the varieties. CARI-UJJAWAL had significantly highest EW (12.72 g) and SI (79.68%). CARI-SUNEHERI was superior with significantly (p<0.01) higher means for SG (1.55 g/cm³) and SP% (12.41%). The overall interior qualities such as Albumen width, albumen height, HU, YD, YH and YI recorded 34.47 mm, 5.28 mm, 88.24, 26.27 mm, 11.32 mm and 0.42, respectively. The HU (88.24) noted in this investigation was found higher to that 85.73 reported by Kul and Seker et al., (2004) but lower than reported by Seker et al., (2008). The higher HU value found in the present study gives an indication of albumen quality, in which a firm and strong albumen with higher density can promote embryo development and successful hatching. All the observations of the internal qualities were coincide with the reports of Kumari et al., (2016) but higher than Daiwko et al., (2013). CARI-UJJAWAL and CARI-SUNEHERI had almost similar values in all the internal quality characters. The YI value recorded was found similar to the 0.36-0.56 notified by Sezer (2008) but higher than Daiwko et al., (2013). The disparities between the results of the present findings and those of other researchers could have incurred due to variation in the genetic structure, flock age, feeding and other rearing managemental practice. Significant (p<0.01) effect of hatch was noticed on majority of egg quality traits. The hens of hatch 3^rd produced slightly heavier eggs (12.84) and correspondingly this hatch has recorded slightly higher means for SW (1.35 g), AW (7.64 g) and YH (11.43 mm), YW (4.67 g) and YP (34.64%). The remaining egg quality traits recorded with non-significant variation among hatches. These findings were comparable to the reports of Kumari et al., (2016) who reported significant difference among the hatches where the hatches at higher ages (7^th or 8^th) has significantly higher values than first and second hatches.
 

 
Heritability estimation
 
Estimates of heritability for egg production and egg quality related traits of three Japanese quail varieties were revealed in Table 3. Regarding ASM, heritability evaluations for all the varieties ranged as low heritable with coefficients from 0.125 to 0.191. This finding was similar to Bahie el-deen et al., (2008); Lotfi et al., (2012) who estimated ASM as a low heritable trait in Japanese quails. Heritability of EN from 8 to 18 weeks of age ranged from 0.048 to 0.582 in present study. Literature revealed the heritability computations of egg number were from 0.09 to 0.48 in laying birds was similar to our reports (Luo et al., 2007; Dana et al., 2011). Low heritability values (0.048 to 0.075) for the initial egg production period in the present study were also reported by Anang et al., (2001); Luo et al., (2007). Heritability evaluations for periods from 10^th to 18^th week egg production were moderate to high (0.217 to 0.582). Wide diversity of heritability estimates in various surveys had been reported and this could be due to reason that EN and ASM were considerably influenced by different environmental factors.
        

 
The egg quality traits values varied and ranged from 0.125 for SI to 0.598 for YH. The heritability estimates found for egg weight were 0.354 (CARI-UJJAWAL); 0.443 (CARI-SUNEHERI) and 0.317 (CARI-BROWN) which were lower than the values reported by Zang et al., (2005); Sezer (2007) but similar to those obtained by Lotfi et al., (2012); Daikwo et al., (2013). In the current study, heritability estimates for SI (0.125 to 0.166) and SW (0.136 to 0.263) were close to those reported by Lotfi et al., (2012). Among the internal quality parameters, albumen quality traits and yolk qualities such as YW, YH and yolk percentage exhibits moderate to high heritability values. The heritability estimates for HU (0.220 to 0.421) reported in this study is higher than reported by Ikeobi (1998) but similar to Zang et al., (2005); Sezer (2008); Daikwo et al., (2013).  The moderate to high estimates of heritability shown by these characteristics suggests that the response to mass selection from these characteristics may be rapid. The low estimate of heritability for YD, SI and SW suggests that additive genetic factors have only little effect on these traits when compared to environmental factors such as feeding management and temperature.
 
Genotypic and phenotypic correlation
 
Correlation between egg production traits
 
Genetic and phenotypic correlations among biweekly egg production traits for all the three varieties were presented in Table 4. Both positive and negative correlation coefficients (genetic and phenotypic) were observed among egg production traits.
 

        
High negative genetic and phenotypic correlations were found between ASM and EN from 8 to 12 weeks of age. Among negative correlation coefficients, the strong negative genetic (-0.816 to -0.930) and phenotypic (-0.815 to -0.982) correlation coefficients were observed between ASM and EN at 8^th week of age in all the three varieties. It means selection for lower ASM (having mature birds in younger age) will improve egg production. Negative genetic correlation between ASM and EN was reported by several studies in Japanese quail (Hidalgo et al., 2011). In all three varieties, high positive genetic (0.845 to 0.996) and phenotypic (0.847 to 0.998) correlations were found between EN at different weeks of age. These were similar to the findings of Lofi et al., (2012) who observed high positive genetic correlations between EN at different periods (0.98 to 0.99). For most of the traits moderate (0.402 to 0.764) to high (0.934 to 0.996) positive correlations were observed between EN at 10^th to 16^th weeks of age. In this present investigation, moderate to high correlation coefficients were found among most of the traits. Therefore appropriate selection aiming at single trait can produce better gain in other traits through correlated response to selection. All the other coefficients show low correlation range (0.030 to 0.402) in both genetic and phenotypic for all the three varieties.
 
Correlations among egg quality traits
 
The genetic and phenotypic correlations among egg quality traits are shown in Table 5. Both positive and negative correlation coefficients (genetic and phenotypic) were observed among the traits. Majority of correlations coefficients were moderate to high in magnitude and positive in all the varieties except shape index. The strong genetic (0.761 to 0.887) and phenotypic (0.845 to 0.965) correlation coefficients were observed between albumen height and albumen width; haugh unit and albumen height (genetic-0.916 to 0.997; phenotypic- 0.899 to 0.998); haugh unit and albumen width (genetic- 0.767 to 0.880; phenotypic- 0.680 to 0.980) in all the three varieties. These values were similar to the findings of Zang et al., (2005); Sezer (2008); Daikwo et al., (2013), who said that the albumen height reflects the most important characteristic of the internal egg quality. Haugh unit scale measures the egg protein quality which depends on albumen height. HU and Albumen height were significant market feature, could be improved by appropriate selection interventions (Individual). Since, albumen height and HU were correlated to each other. The positively significant genetic (0.698 to 0.727) and phenotypic (0.512 to 0.883) correlation between yolk weight and yolk diameter suggests that selection for increased yolk diameter would increase yolk weight. These were similar to the findings of Sezer (2008); Daikwo et al., (2013). Similarly, the yolk height shows positive correlation with yolk diameters in both genetic (0.470 to 0.506) and phenotypically (0.437 to 0.665) in all the three varieties. These associations of the yolk could benefit better to increase the hatchability and chick quality by selection methods because the yolk is the concentrated source of nutrition for the embryo Egg shape index and egg weight are important traits from the point of mechanical handling of eggs. Egg weight had negative genetic (-0.315 to -0.422) and phenotypic (-0.484 to -0.785) correlation with egg shape index. Similar results have been reported by reported by Sezer (2007); Narinc et al., (2015). The other characters showed low positive correlation coefficients with its respective traits. The present findings were similar to Kumari et al., (2016) who reported that almost all the egg quality traits (external and internal) were associated themselves positively in direction but low to high in magnitude. 
 

The economic returns from a poultry enterprise are determined to a large extent by the ASM, the number of eggs they produce within a certain time interval along with its egg quality traits. Among all the varieties, CARI-UJJAWAL recorded higher Least squares mean values in traits such as ASM, EN upto 8th week. CARI-SUNEHERI matured later but showed good production at EN at 14^th week. In the egg quality traits, both CARI-UJJAWAL and CARI- SUNEHERI exhibited similar values in most of the traits. Among egg production and among egg quality traits, most of the traits exhibit higher correlation coefficients between each other. Selection of any trait could be beneficial in terms of correlated gain in other traits. This informative record can also be included in the selection criteria in CARI-UJJAWAL, CARI-SUNEHERI and CARI-BROWN for effective selection in egg production and egg quality traits.