Estimation of Genetic Parameters for Economic Traits in Korean Native Chickens

Heritabilities and genetic correlations of economic traits were estimated with a multiple-trait animal model on 5 different strains of Korea Native Chickens (KNC): Red Brown (RB), Yellow Brown (YB), Gray Brown (GB), Black (B) and White (W). The data used for this study were collected from the Daejeon branch of the National Livestock Research Institute and included 11,233 performance records and 12,729 individual animals. DFREML and SAS BASE/STAT packages were used to estimate genetic parameters and descriptive statistics. The estimated heritabilities for strain RB, YB, GB, B and W, respectively, for age at 1st egg were 0.24, 0.27, 0.12, 0.32 and 0.18; for body weight at first egg were 0.39, 0.43, 0.38, 0.52 and 0.57; for body weight at age of 270 days were 0.43, 0.51, 0.30, 0.52 and 0.67; for egg weight at first egg were 0.08, 0.13, 0.07, 0.06 and 0.07; for egg weight at age of 270 days were 0.37, 0.43, 0.22, 0.34 and 0.41; and for number of eggs laid by age of 270 days were 0.24, 0.25, 0.37, 0.36 and 0.30. The genetic and phenotypic correlations were also estimated. (Asian-Aust. J. Anim. Sci. 2006. Vol 19, No. 3 : 319-323)


INTRODUCTION
The first introduction of Korean Native Chicken (KNC) was not clear although it was assumed to be introduced through south and north China about 2,000 years ago.KNC are less fatty and higher protein content compared to foreign breeds.Therefore it is very popular to domestic consumers.The initial endeavor to establish the pure lines of KNC was started in 1980 by governmental research institutes by way of collecting them being spread nationwide and the phenotypic characteristics of 5 KNC strains were shown in Table 1.
Pursuing an efficient selection and genetic improvement of chickens, various authors have studied and published on estimation of genetic parameters on egg production and growth (Lush, 1948;Lerner and Cruden, 1951;King and Henderson, 1954;Kinney, 1969;McClung et al., 1976).Han et al. (1986) published on genetic parameters of economic traits in KNC named O-Gol and Jung et al. (1992) reported the estimated heritabilities and genetic correlations among economic traits on KNC.Since 1950's, numerous studies have been reported on the heritability estimates for the age at first egg, egg production, and egg weight for the layers.But there have been little studies for established pure strains of KNC.Mixed linear models with BLUP property have been of primary use for estimation genetic parameters and genetic evaluation.Recently the random regression model has been widely used for those purpose (Yang et al., 2004).A molecular approach to detect major genes affecting the economic traits for chicken has been studied by Mannen et al. (2004).In this study, heritabilities and genetic correlations on the economic traits of established KNC pure strains were estimated with multiple trait animal models.where, y ij : j th observation of i th strain, S i : j th strain effect, and e ij = random residuals.
Strain least squares means of each trait were compared with pair-wise manner with SAS GLM's PDIFF option (SAS, 2000).
Multiple trait individual animal model was used to estimate heritabilities and genetic correlations among the 6 traits of each strain.The linear model used for this analysis was given as: where, y ijk : record of k th individual measured in j th hatchday for i th trait, hatchday ij : fixed effect of j th hatchday for i th trait, a ijk : additive genetic effect of k th individual in j th hatchday for i th trait and, e ijk = random residuals.
The DFREML version 3.1 (Meyer, 2001) package were used for the genetic parameter estimation and SAS BASE/STAT package was also used to get descriptive statistics of data.The estimates obtained from previous run of 2 traits pair-wise analysis were used as starting values for six trait genetic parameter estimation and AI-REML was used for searching algorithm.In Table 3, levels of fixed and random effect were listed by trait and strain.The levels of fixed effect for body weight at first egg trait were smaller than other traits because body weights at first egg were not taken in 1995.

Phenotypic differences among strains
The means, their standard errors of each traits and pairwise comparisons among strains were computed with MEANS and GLM procedure with PDIFF option of SAS 8.2 package for each trait and strain (Table 2).For all six traits, the strain effect were significant at p>0.05 and least squares means of each trait from different strains revealed differences of strains.

Genetic parameters
The heritabilities, genetic correlations and phenotypic correlations estimated with six trait multiple animal model were shown in Table 3, 4, 5, 6 and 7 for strain RB, YB, GB, B and W, respectively.
The estimated heritabilities for Age at 1st egg were 0.24, 0.27, 0.12, 0.32 and 0.18 for strain RB, YB, GB, B and W, respectively.The results of the study conformed with the finding of Lee, et al. (1998) using of KNC with an estimated heritability for age at first egg, 0.13-0.25.Although report by Han and Ohh (1975) was slightly higher, 0.20-0.45 in their study using short Comb White Leghorn (SCWL) Korean laying stocks.The estimated heritability of strain B was in the range of previous estimates in White Leghorn breed (Emslay et al., 1977;Hagger and Abplanalp, 1988).However, the estimates from all strains studied were lower than previous estimates of 0.40 by Craig et al. (1972) and 0.47 by Singh et al. (1972) in White Leghorn breed, and much lower than 0.58 reported by Tixier-Boichard et al. (1995) in Brown Leghorn breed.
The estimated heritabilities for Body weight at first egg were 0.39, 0.43, 0.38, 0.52 and 0.57 for strain RB, YB, GB, B and W, respectively.However, lower heritability values, 0.23-0.39,were reported by Lee et al. (1998) in their study of 4 strains of KNC.These estimates were similar to those of 0.47 reported by McCling et al. (1976).
The estimated heritabilities for Body weight at age of 270 day were 0.43, 0.51, 0.30, 0.52 and 0.67 for strain RB, YB, GB, B and W, respectively.Lower heritability values (0.13-0.49) were published by Lee et al. (1998).For YB, B and W strains, the estimated heritabilities were somewhat lower than previous estimates of 0.60 by Buchel (1970), 0.58 by McClung et al. (1976), 0.59 by Tixier-Boichard et al. (1995), 0.62 by Vaccaro and Van Vleck (1972) in White Leghorn breed.However, the estimates of all strains in this study were much lower than the estimate of 0.73 reported   which indicates this trait was, at large, environment dependent.For most economic traits of KNC, their heritabilities are of moderately large sizes and will enhance a great potential for genetic improvement.

Table 1 .
Phenotypic characteristics of KNC

Table 2 .
Means and their standard errors by trait and strain

Table 3 .
Estimated heritabilities, genetic correlations and phenotypic correlations in strain RB

Table 4 .
Estimated heritabilities, genetic correlations and phenotypic correlations in strain YB Heritabilities are on the diagonal, genetic correations are above and phenotypic correlations are below the diagonal.

Table 5 .
Estimated heritabilities, genetic correlations and phenotypic correlations in strain GBHeritabilities are on the diagonal, genetic correations are above and phenotypic correlations are below the diagonal.