略阳乌鸡体重和产蛋数性状遗传参数估计

Estimation of Genetic Parameters of Body Weight and Egg Number Traits of Lueyang Black-Boned Chicken

【目的】略阳乌鸡是陕西省特有的家禽品种,该品种具有体型大、肉质好、氨基酸含量丰富、对林地散养适应性强的优点,但也存在生长缓慢,产蛋性能差的不足。为此,在系统测定略阳乌鸡生产性能的基础上,开展对体重和产蛋性状遗传参数的估计,阐明遗传效应对上述性状的调控作用及性状间的遗传关系,期望为这些性状的选育奠定理论基础。【方法】对略阳乌鸡蛋用系一世代71个半同胞家系799只公鸡和804只母鸡6、10、14、20周龄和开产日龄体重进行测定,以个体为单位记录从开产到31、35和40周龄产蛋数,以四分位数±1.5倍四分位距为界删除异常值,更正性别记录错误。以性别为固定效应,育种值为随机效应用单变量动物模型估计各性状遗传力,用双变量动物模型估计性状间遗传相关,用逆伽玛分布指定育种值和残差项方差先验分布,用贝叶斯算法执行130000次迭代,弃去前30000次迭代结果,以100为间隔抽取1000个估计值获得方差和协方差后验分布,计算各性状遗传力和性状间遗传相关。用R语言PerformanceAnalytics软件包chart.Correlation命令计算性状间表型相关。【结果】略阳乌鸡6、10、14、20周龄公鸡体重为(0.56±0.07)、(1.07±0.13)、(1.56±0.19)、(1.97±0.21)kg,母鸡体重为(0.47±0.06)、(0.86±0.12)、(1.18±0.16)、(1.48±0.19)kg,开产体重为(1.68±0.23)kg;31、35和40周产蛋数为(31.2±11.5)、(42.5±16.7)和(54.7±20.4)枚。体重遗传力随年龄逐渐减小,分别为0.74、0.76、0.63、0.54和0.52,置信区间在0.25-0.33之间。产蛋数遗传力为0.27、0.25和0.26,置信区间在0.35-0.42之间。10、14、20周龄体重间维持中等偏上(0.52-0.68)的遗传相关性,但6周龄体重(0.21-0.52)和开产体重(0.21-0.46)与各时间点体重遗传相关性较弱。体重间遗传相关系数置信区间在0.13-0.34之间。在3个时间点产蛋数间遗传相关系数趋近于1,置信区间在0.03-0.06之间。体重和产蛋数间遗传相关系数均不显著。在时间维度上,各体重性状间表型相关系数在0.43-0.90之间(P<0.001),产蛋数性状间表型相关系数在0.79-0.94之间(P<0.001)。6-20周龄体重与产蛋数间维持了弱(0.023-0.15)正相关关系,但开产体重与产蛋数存在弱负相关关系(-0.17--0.14)。【结论】首次估计了略阳乌鸡品种特异性的遗传参数,发现略阳乌鸡体重性状主要受遗传效应调控,而产蛋数性状受环境影响更大,阐明了早期与晚期性状间、体重与产蛋数间的遗传关系,为早期选种和多性状育种奠定了理论基础。这些结果建议在略阳乌鸡群体中对体重性状表型选择有望取得良好效果,但对产蛋数性状应建立纯系利用杂种优势;体重和产蛋数间不存在负遗传相关关系,可同时对两个性状选育提高。

【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 1st quantile-1.5×interquantile range and higher than 3rd 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 1000 posterior estimates which were produced using Bayesian algorithm by running 130000 iterations of which the first 30000 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.