Genetic Improvement of Egg Production and Associated Traits in Egg Type Japanese Quail

Japanese quail farming is becoming popular in commercial poultry sector for meat and egg production. Rapid growth rate, early sexual maturity, high rate of egg laying and much lower feed consumption are the advantage of Japanese quail farming. Japanese quails are rapidly gaining in popularity for its commercial exploitation and in near future may acquire an important segment in rapidly growing Indian poultry industry (Mishra and Shukla, 2014). Selection is a powerful means to increase body weight and rate of gain in Japanese quails. Japanese quail is suggested as a pilot animal for genetic studies because of its shorter generation interval and the economy of production resulting from faster growth rate and its smaller body size. Nowadays demand for the Japanese quail eggs is also increasing due to cheaper cost and is alternative to chicken eggs. Developing separate egg type Japanese quail is a need of the hour to propagate layer quail farming which fulfill the demand of egg production and nutritional security. Most of the selection studies in Japanese quail have focused on increasing body weight; on the other hand, only a limited number of studies were aimed at improving egg production (Nestor et al., 1983, Maeda et al., 1999 and Minvielle et al., 2000). Beside egg production performance, egg quality (both external and internal traits) is also important for human consumption and for hatcheries.  Considering the above, a research work was initiated during the year 2014 to develop egg type Japanese quail  from Nandanam quail 3 (base population) with genetic selection and its effects on body weight, egg production and reproductive performance were assessed in all six generations.

Breeding programme adopted
 
Genetic improvement for egg production performance of Japanese quail was carried out for six generations at Poultry Research Station (PRS), Tamil Nadu Veterinary and Animal Sciences University, Chennai-51 between 2014 and 2019. The base population of 600 females was derived from Nandanam quail 3 available in PRS. Individual selection for the improvement of body weight and family selection with shift mating (60 males+240 females) for higher egg production with 1:4 ratio was carried out continuously for six generations to increase the egg number and body weight simultaneously. A total 2000 day-old chicks in three hatches were taken as replacement population in each generation. The population size of 720 females (12 female/ sire families) and 900 males (15 male/ sire family) were selected based on pedigree selection from 60 sires families. Sire family selection for egg production in females and sib selection for body weight in males were adopted as a selection aids at 6 weeks of age. Egg production up to 30 weeks periods were used as selection criteria in family selection for egg production and egg production performance was recorded from six to 46 weeks. The selection pressure was 1 in 4 for females and 1 in 16 for males. Individual selection on fourth week was considered as a selection criteria for improving body weight. To assess the effect of short-term selection on various parameters such as day old chick weight, 4, 6 and 10th week body weight, feed conversion ratio, hen day and hen housed egg production, liveability, fertile and total egg hatchability, time-trend and regression analysis were carried out as per standard statistical methods. (Snedecor and Cochran, 1989).

Body weight performance
 
The day-old chick weight of all six generations ranged from 9.2 to 9.28 g (Table 1). Although the time trend analysis revealed a positive change of 0.011 g per generation, which was insignificant (P>0.05) and less reliable (R2=0.52). The 4^th and 6^th week mean body weight of the first generation was 163.46 g and 178.82 g respectively, which increased to 166.16 g and 181.35 g respectively in 6th generation.  Similarly, the 10^th week female body weight in 1^st generation increased from 241.12 g to 243.35 g at 6^th generation. The linear regression analysis of fourth week body weight in males over generations revealed significant (P<0.01) increment of 0.59 g per generation. A very high R² value (0. 83%) indicates excellent goodness of fit and reliability of linear regression model over observed values.  Similarly, the fourth week body weight in females also had a positive change (b= 0.89g) per generation with high degree of goodness of fit (R²= 0.93). The analysis of pooled data for fourth week body weight indicated a genetic gain of 0.60 g per generation, with an excellent coefficient of determination (0.92%). Similarly, the linear regression analysis of sixth week body weight in males and females over generations revealed significant (P<0.01) increment of 0.26 g and 0.76 g per generation, respectively. Although the goodness of fit of linear regression was poor (R²= 0.47%) males, a high value of 0.87% was recorded in females indicating excellent goodness of fit and reliability. The analysis of pooled data for sixth week body weight indicated a genetic gain of 0.51 g per generation, with an exceptionally good coefficient of determination (0.93 %). The 4^th and 6^th week body weights recorded in this study was higher than those reported by Mohammed et al., (2006), Hyankova et al., (2008), Sakunthaladevi et al., (2010), Khaldari et al., (2010), Hossain et al., (2015) and Subhashini et al., (2018a) in Japanese quail. In our study, it was evident that the mean body weight increased in the course of selection. However, a higher phenotypic response of 13.23 g and genetic repose of 9.69 g has been reported by Churchil et al., (2019a) in Japanese quails.


 
Liveability (%)
 
The mean liveability ranged from 92.1 to 93.53% and that of 7 to 46 weeks, from 94.25 to 95.50% (Table 2). The linear regression analysis of liveability during 0 to 6 weeks of age revealed an increment of 0.34% (P<0.05) per generation with high degree of goodness of fit of regression equation with the observed values. On the other hand, the livability from 7 to 46 weeks of age over generations revealed insignificant (P>0.05) change of only 0.11%. The per cent liveability observed in our study is comparable with Subhashini et al., (2018) and Ahmad et al., (2018) who recorded 92.50% and 87.81% respectively during 0-4 weeks of age in selected line of quails. Improvement in fitness traits in each generation observed in our study might be due to application of intense selection resulted in better exploitation of superior genes, which leads to increased liveability as reported by Hussain et al. (2013).

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Feed consumption
 
The mean feed consumption and FCR (Table 3) during 0 to 6 weeks of age was 452.02 g and 2.51 respectively. The feed consumption from 0 to 6 weeks of age showed positive change of very low magnitude (b= 2.68 g; R2= 0.53; P>0.05) over generations to reach 459.01 g in sixth generation from 116.50g at first generation. Similarly, low magnitude insignificant positive change was also observed with feed consumption from 7 to 46 weeks of age (b= 0.063 kg g;  R2= 0.15; P>0.05) from first (9.80 kg) to sixth (10.50 kg) generation.  Similar reports was observed by Ahmad et al., (2018) who recorded 430.25 gm of feed intake with 2.40 FCR during 0 to 4 weeks of age in selected line of Japanese quail and reported that pedigree birds had significantly better FCR compared with mass-selected and random-bred control birds. Further, Subhashini et al., (2018a) observed a cumulative feed efficiency of 2.36 during 4th week in Japanese quail. In addition, Hussain et al.  (2013) observed that a selected line had better feed efficiency than the control group.

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Egg production (%)
 
The age at sexual maturity in egg type Japanese quail was reduced from 42 in first generation to 40 days in sixth generation (Table 4). The change was significant (P<0.05) in negative direction (b= -0.40 day; R2= 0.70) over generations. Hossain et al., (2015) observed an average sexual maturity of 40 days in layer Japanese quail in Bangladesh. Studies reported a wide range of age at sexual maturity (42 to 56 days) in Japanese quail which is in harmony with the present investigation (Devi et al., 2010; Monica et al., 2020). The decreasing age at sexual maturity as a correlated response for improvement in egg production in poultry is an established phenomenon as these traits are negatively correlated (Narayanankutty et al., 2008, Churchil et al., 2019b).

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The per cent hen housed egg production from 6 to 46 weeks of age increased from 202 to 220 eggs during the course of selection. Linear regression analysis revealed that the increase was significant (P<0.01), with appreciable magnitude in positive direction (b=3.77) with excellent of goodness of fir (R²=0.97). Similarly, the hen day egg production during this period also showed significant (P<0.01) upward trend (b=3.17) over generations with the trend line showing excellent goodness of fit with observed values (R² = 0.96). With this degree of improvement he hen day egg production reached to 225 eggs in sixth generation from 206 eggs in the first generation. Similar to our finding, Hossain et al., (2015) observed that the hen day egg production of 89 % during 45-49 weeks and 88 % during 50-52 weeks of age in Japanese quail. Durmus et al., (2017) found that, the egg production of the layer lines Japanese quail ranged from 44.60 to 57.01 eggs for a 2-month period and from 245.4 to 332.7 eggs for 13 months. Further, Narinc et al., (2013) found that the mean value of egg production in a control Japanese quail line was 216 eggs for 52 weeks. In another study, Krishna Daida and Sahitya Rani (2017) found that broiler Japanese quail variety attain the age at sexual maturity between 55.79 to 56.53 days and the hen day egg production was 31.23, 69.91 and 54.81 % in 16^th, 32^nd and 46^th week respectively.
 
Egg weight
 
Although the change was not significant (P>0.05), the mean egg weight showed a declining trend over generations during selection (b= - 0.02) to reach 12.14 g in sixth generation from 12.20g in the first generation. The reduction in egg weight in short term selection has been reported earlier (Nestor and Noble, 1995). The reduction in egg weight in poultry selected for egg number has been reported already as these traits are negatively correlated (Churchil et al., 2019b).
 
Reproductive performance
 
The parameters like fertility and hatchability of eggs (Table 5) were not much affected due to selection. The fertility of eggs in the first generation was 79.78%, which is almost same across the generations with minimum and maximum values as 78.76 and 80.17% respectively. Similarly, hatchability also showed no marked changes due to selection with values varying from 64.18 to 64.51% across the generations. The regression analysis also revealed insignificant (P>0.05) change of fertility (b = 0.17; R2 = 0.34) and hatchability (b = 0.04; R2 = 0.43) values across generations. Similar to this study Asasi and Jaafar, (2000) found an average fertility of 75% and hatchability of 65% up to 52 weeks of egg production.

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Egg quality parameters
 
The egg quality parameters such as egg weight, shape index, specific gravity, albumen index, yolk index, Haugh unit score, yolk colour, shell thickness and shell percentage values presented in Table 6 were comparable with that of previous studies (Kumari et al., (2016); Subhashini et al., (2018 b); Monika et al., (2020) in different strains of Japanese quails.

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It can be concluded that the multi stage selection can improve the body weight and egg production in Japanese quails despite the fact these traits are negatively correlated. This type of selection programmes can be adopted for exploiting body weight and egg number simultaneously to develop dual purpose Japanese quails.

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