Genetic Evaluation of Body Weights and Egg Production Traits Using a Multi-Trait Animal Model and Selection Index in Thai Native Synthetic Chickens (Kaimook e-san2)

Abstract

To improve the genetics of both growth and egg production, which are limitations in purebred native chickens, new genetic lines can be developed using an appropriate genetic approach. The data used in this study included 2713 body weight (BW0, BW4, BW6, BW8, and BW10), breast circumference (BrC6), chicken age at first egg (AFE), and egg production (240EP, 270EP, 300EP, and 365EP) records covering the period 2015 to 2020. A multi-trait animal model with the average information-restricted maximum likelihood (AI-REML) and a selection index was used to estimate the variance components, genetic parameters, and breeding values. The results showed that males had significantly higher weights than females (p < 0.05) from 4 to 10 weeks of age and that this difference increased over the generations. The differences between BW0 and BrC6 by sex and generation were not significant (p > 0.05). The estimated heritability of body weight ranged from 0.642 (BW0) to 0.280 (BW10); meanwhile, the estimated heritability of BrC6 was moderate (0.284). For egg production traits, the estimated heritability of 240EP, 270EP, 300EP, and 365EP was 0.427, 0.403, 0.404, and 0.426, respectively, while the estimated heritability of AFE was 0.269. The genetic and phenotypic correlations among the growth traits (BW0 to BW10) were low to highly positive. The genetic and phenotypic correlations between growth (BW0 to BW10) and BrC6 traits were positive, and the genetic correlations between BW6 (0.80), BW8 (0.84), BW10 (0.93), and BrC6 were strongly positive. Genetic correlations among the egg production traits (240EP, 270EP, 300EP, and 365EP) were low to highly positive and ranged from 0.04 to 0.86. The genetic correlations between AFE and all egg production traits were low to moderately negative and ranged from -0.14 to -0.29. The positive genetic correlations between body weight (BW6, BW8, and BW10) and egg production traits were found only in 240EP. The average genetic progress of body weight traits ranged from -0.38 to 30.12 g per generation for BW0 to BW10 (p < 0.05); the genetic progress was 0.28 cm per generation for BrC6 (p > 0.05). The average genetic progress of cumulative egg production traits ranged from 4.25 to 12.42 eggs per generation for 240EP to 365EP (p < 0.05), while the average genetic progress of AFE was -7.12 days per generation (p < 0.05). In conclusion, our study suggests that the body weight at six weeks of age (BW6), breast circumference at six weeks of age (BrC6), cumulative egg production at 240 days of age (240EP), and age at first egg (AFE) are the traits that should be used as selection criteria, as they have a positive effect on the development of growth and egg production.

Keywords: Thai indigenous chicken; age at first egg; chicken breast meat; egg number; genetic trend; growth.

Figure 1

Morphology of male (A) and female (B) KM2 chickens.

Figure 2

Least-squares means of body weight and breast circumference traits separated by (a) sex and (b) generation in KM2 chickens; a, b, c, d, e: Means for the trait with different letters differ significantly at p < 0.05. BW0—birth weight; BW4—body weight at 4 weeks of age; BW6—body weight at 6 weeks of age; BW8—body weight at 8 weeks of age; BW10—body weight at 10 weeks of age; BrC6—breast circumference at 6 weeks of age; G—generation.

Figure 3

Least-squares means of age at first egg and cumulative egg production traits separated by generation in KM2 chickens; a, b, c, d, e: Means for the same trait with different letters differ significantly at AFE—age at first egg; 240EP—cumulative egg production at 240 days of age; 270EP—cumulative egg production at 270 days of age; 300EP—cumulative egg production at 300 days of age; 365EP—cumulative egg production at 365 days of age; G1-G6—1st generation to 6th generation of chicken.

Figure 4

Genetic progress per generation for (a) body weight and breast circumference and (b) age at first egg and cumulative egg production traits in KM2 chickens. ns is not significant difference (p > 0.05); * is significant value within trait by generation (p < 0.05). BW0—birth weight (g); BW4—body weight at 4 weeks of age (g); BW6—body weight at 6 weeks of age (g); BW8—body weight at 8 weeks of age (g); BW10—body weight at 10 weeks of age (g); BrC6—breast circumference at 6 weeks of age (cm); AFE—age at first egg (day); 240EP—cumulative egg production at 240 days of age (egg); 270EP—cumulative egg production at 270 days of age (egg); 300EP—cumulative egg production at 300 days of age (egg); 365EP—cumulative egg production at 365 days of age (egg); The blue bar represents a positive numbers for the genetic progress for each trait; The red bar represents a positive numbers for the genetic progress for each trait.

Figure 5

Top 20% of the selection index values and accuracy of the selection index values in male and female KM2 chickens; acc—the accuracy of selection index; The blue bar represents a selection index value for the male; The red bar represents a selection index value for the female.