Introduction

The Japanese quail, Coturnix japonica is known to have been domesticated since the 12^th century AD in Japan, mainly for its ability to sing. Intensive production of the species started in Japan in the 1920s. The first egg lines were then developed by selection (Wakasugi, 1984). They were successfully introduced from Japan to America, Europe, the near and Middle East between the 1930s and 1950s, where specific lines were bred for egg and meat production. Extensive research on Coturnix japonica has showed that it was a valuable animal for avian research (Woodard et al., 1973). It has expanded from avian science-related topics to biology and medicine, as this bird could be kept easily in relatively large numbers in a small facility and be used as a model animal for a wide variety of work, from embryology (Le Douarin et al., 1969) to space-related sciences (Orban et al., 1999).

Growth is moderately to highly heritable and can be rapidly improved through individual phenotypic selection. However, growth is a dynamic process that involves both an increase in mass and synchronous differentiation and maturation of many tissues. Consequently, selection results are highly dependent on the  methods employed, including the age of primary selection,  intensity of selection, selection emphasis placed on correlated traits and the environment (including nutritional aspects) under which selection is exercised (Emmerson, 1997). A selection experiment was designed. Individual phenotypic selection was contemplated to facilitate development of superior breeder flock suitable for production of optimum number of fast growing commercial meat type Japanese quails. The study was also designed to obtain an understanding of the relationship between selection age and growth with the following objectives, viz., to evaluate selection for juvenile, fourth-week and sixth-week body weights in Japanese quail.

Absolute body weight gain makes, however, no allowance for differences in body frame (i.e. skeletal structure), nor does weight, by itself, accurately reflect a bird’s condition. Although having the same body weight, a bird with a large frame will be in a poorer condition than a bird with a smaller frame. To correct for this bias, relative body weight gain may be used (Livestock system research manual, 1990).

Materials and Methods

The study was carried out at the Institute of Poultry Production and Management, formerly known as Poultry Research Station, Tamilnadu Veterinary and Animal Sciences University, Nandanam, Chennai, India. A Japanese quail (Coturnix japonica) population, maintained at the institute formed the base population for this study. The foundation stock for the three selected and an unselected control populations was from a random mating Japanese quail line maintained at the Institute of Poultry Production and Management, Chennai. The line had no known history of artificial selection except for a short period during 1989 to 1992 when the population was subjected to selection on the basis of body weight at four weeks of age for four generations under two different nutritional environments of high and low protein diets. From the foundation stock, one hundred and eighty males and equal number of females were randomly selected, wing banded, weighed, and randomly assigned to four groups to have 45 pairs in each of the four groups. The breeder males and females were maintained in cages under single pair mating. Hatching eggs were collected and set for hatch. Chicks hatched from three groups were subjected to individual phenotypic selection for body weight at different ages.  One group (SWL) was selected for high body weight at two weeks of age, the other (FWL) for high body weight at four weeks of age. The third group (LWL) was subjected to two stage selection with the initial selection practised at four weeks of age for high body weight, followed by selection for low relative body weight gain between four to six weeks of age. The fourth group (COL) was maintained as control line with random selection of parents.

The number of hatches obtained and the total number of progenies produced in the three selected lines and control were 2176, 1780, 2331 and 2343, respectively in S₀, S₁, S₂ and S₃ generations. Only those data of progenies with intact wing bands and whose sexes were phenotypicaly identifiable were included in the study. One of the four groups formed in the base generation (S_o) was treated as control line and raised separately along with the selected populations (other three lines) in each generation to observe and account for environmental influences. Single pair mating was followed with females assigned at random to individual males with the restriction that no full sib mating was permitted.

Measurement of the Traits

Body weight gain: The data of progenies whose wing bands were intact, sexes were identifiable and also only those with body weight records from hatch to six weeks of age were included in the study.

Relative body weight gain (RGW %): The relative body weight gain (RGW) was computed by using the following formula as suggested by Kratochvílova et  al. (2002).

The RGW during 1^st (RGW1), 2^nd (RGW2), 3^rd (RGW3), 4^th (RGW4), 5^th (RGW5) and 6^th (RGW6) week of age were computed based on the ratio of difference in body weights between two successive intervals to the body weight at initial interval and expressed in per cent.

The transformation of per cent data into square root arc-sin values was undertaken as per Snedecor and Cochran (1967).

Statistical analysis: The data generated on body weight for age were corrected for the fixed effects of line, generation, sex and hatch by the least squares analysis (Harvey, 1979) using the following linear model based on pooled data.

Duncan’s multiple range test (Duncan, 1955) was employed to make all pair wise comparisons of means.

Results and Discussion

The results of least squares analysis of variance of RGW based on pooled data presented in Table – 1. The overall least squares mean for RGW during 1, 2,3,4,5 and 6 weeks of age were 377.68±3.28, 108.88±1.87, 56.28±1.43, 29.23.10±0.59, 15.14±0.39 and 11.23± 0.30 g, respectively Table- 2.

The least squares means of RGW ranged from 374.39±3.69 at RGW1 to 11.58±0.33 per cent at RGW6 in SWL line, 383.21±3.58 to 11.10±0.32 per cent in FWL line, and 374.51±3.78 to 10.85±0.34 per cent LWL line respectively. In COL line the means RGW varied from 378.60 ±3.81 of RGW1 to 11.41±0.34 per cent of RGW6.

Table : 1 Least squares analysis for variance of relative weight gain

*Significant at P<0.05; ** Significant at P< 0.01

The least square means of RGW during first, second, third, fourth, fifth and sixth week of age in S₀ were 370.37±3.85, 124.25 ± 2.20, 44.51±1.68, 24.15±0.0.69, 16.94±0.45 and 10.48±0.35 per cent. The corresponding means were 383.81±3.91, 115.03±2.23, 42.62±1.70, 31.90±0.70, 18.23±0.46 and 11.99±0.35  per cent in S₁, 374.04 ±3.76, 92.63 ±2.15, 75.08±1.64, 30.18±0.67, 12.25±0.44 and 12.22 ±0.34  per cent in S₂ and 381.89±3.42, 103.61±1.96, 62.90±1.49, 30.68±0.61, 14.14±0.31 and 10.28±0.31  per cent in S_3.

Least squares means of per cent relative body weight gain indicated that the Japanese quail chicks established a very high phenomenal rate of growth during first week of age which averaged 377.68 per cent over weight at hatch. It slowed down drastically to 108.88, 56.28, 29.23, 15.14 and 11.23 per cent during 2^nd, 3rd, 4th, 5th and 6^th week of age.

Table : 2 Least squares means of relative body weight gain (%) at various ages (0-6 weeks) on pooled data

Means with different superscripts within each column, trait and effect differ significantly (P<0.05)

As indicated by absolute body weight gain, the relative weight gain per cent also becomes very minimal as age advances beyond three weeks of age. Hence, depending on the market preference, the age at marketing of Japanese quail may be advanced from fifth week to at least four weeks of age, so that wastage of expenditure in feed could be saved as the rate of gain becomes very poor afterwards.

Kucukyilmaz et al. (2001) suggested that five weeks would be the ideal age for selection as per cent of body weight gain was lower at six weeks compared to five weeks.

Since relative body weight gain became very poor after four weeks, it is suggested that selection for body weight in Japanese quail meat strains could be advanced to four weeks of age.

References

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