Abstract:

【Objective】Lueyang black-boned chicken (LBC) is an indigenous breed originating from Shaanxi province of China. The breed has large adult body weight, high meat quality, abundant contents of amino acids in meat and excellent adaptation to the free-range system in the forest. But the breed has poor performance of growth and egg production. We measured body weight (BW) and egg number (EN) of LBC at different ages. Based on these phenotypic data we evaluated genetic parameters of BW and EN traits. The aim of this study is to elucidate effect of genetic factors on these traits and genetic relationship among them, thus forming a theory foundation to breeding programs of LBC.【Method】BWs at 6, 10, 14, 20 weeks of age and first egg of 799 cocks and 804 hens from 71 half-sibling families of generation 1 of LBC breeding population and individual ENs from first egg to 31, 35 and 40 weeks of age were measured. Data lower than 1^st quantile-1.5×interquantile range and higher than 3^rd quantile + 1.5×interquantile range was deleted prior to statistical analysis. Errors in sex records were corrected. Heritabilities were estimated using a univariate animal model where sex was designed as the fix effect, and additive genetic effect was designed as random effect. Genetic correlations among traits were estimated using a bivariate animal model. Inverse gamma distributions were used as the prior distributions for variance components of random and residual effects. Posterior distributions of variance components were obtained based on 1 000 posterior estimates which were produced using Bayesian algorithm by running 130 000 iterations of which the first 30 000 were discarded in ‘burn-in’ period and the rest was sampled every 100 iterations. Heritabilities and genetic correlations were calculated according to posterior variance components. Phenotypic correlation among traits was calculated using chart.Correlation command in PerformanceAnalytics library of R.【Result】BWs of LBC cocks were (0.56±0.07), (1.07±0.13), (1.56±0.19), (1.97±0.21) kg and BWs of hens were (0.47±0.06), (0.86±0.12), (1.18±0.16), (1.48±0.19) and (1.68±0.23) kg at 6, 10, 14, 20 weeks and first egg. ENs were 31.2±11.5, 42.5±16.7 and 54.7±20.4 at 31, 35 and 40 weeks. Heritabilities of BWs at 6, 10, 14, 20 and first egg that were 0.74, 0.76, 0.63, 0.54 and 0.52 generally decreased with increasing age. Ninety-five percent confidence interval of BW heritabilities ranged from 0.25 to 0.33. Heritabilities of ENs at 31, 35 and 40 weeks were 0.27, 0.25 and 0.26 with 95% confidence interval varying between 0.35 and 0.42. Genetic correlation among 6, 10 and 14 week BWs were moderate to high (0.52-0.68). But BWs at 6 week (0.21-0.52) and first egg (0.21-0.46) showed relatively week genetic relationship with other BWs. Ninety-five percent confidence interval of genetic correlation coefficients among BW traits ranged from 0.13 to 0.34. Genetic correlation coefficients among EN traits approached to 1 with 95% confidence interval ranging from 0.03 to 0.06. BWs and ENs did not show any significant genetic relationship. On the temporal dimension phenotypic correlation coefficients varied between 0.43 and 0.90 (P<0.001) for BW traits and between 0.79 and 0.94 (P<0.001) for EN traits. There was weak (0.023-0.15) positive correlation between BWs at 6-20 weeks and ENs. But the BW at first egg showed weak negative correlation (-0.17-0.14) with ENs. 【Conclusion】This represents the first study specifically estimating genetic parameters for LBC. The data shows that BW traits of LBC are predominately determined by genetic factors. In contrast, ENs are more influenced by environmental factors. Results from genetic correlation analysis elucidated the genetic relationship between early and late traits, and between growth and reproduction in LBC, which provide a solid foundation for early selection and multiple-trait breeding programs. High heritabilities showed by BWs suggest that the phenotypic selection of BWs could significantly increase the growth rate of LBC. However it might be more reasonable to breed pure lines and take advantage of heterosis to increase egg yield of LBS. Genetic independence between BWs and ENs suggests that it is feasible to simultaneously improve two traits in the LBC.

Key words: Lueyang black-boned chicken, body weight, egg number, heritability, genetic correlation