Departamento de Zootecnia, Universidade Estadual Paulista, Jaboticabal, São Paulo, Brazil 14884-900.
J Anim Sci. 2010 Dec;88(12):3809-13. doi: 10.2527/jas.2009-2127. Epub 2010 Jul 23.
Scrotal circumference data from 47,605 Nellore young bulls, measured at around 18 mo of age (SC18), were analyzed simultaneously with 27,924 heifer pregnancy (HP) and 80,831 stayability (STAY) records to estimate their additive genetic relationships. Additionally, the possibility that economically relevant traits measured directly in females could replace SC18 as a selection criterion was verified. Heifer pregnancy was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 d. Females were exposed to sires for the first time at about 14 mo of age (between 11 and 16 mo). Stayability was defined as whether or not a cow calved every year up to 5 yr of age, when the opportunity to breed was provided. A Bayesian linear-threshold-threshold analysis via Gibbs sampler was used to estimate the variance and covariance components of the multitrait model. Heritability estimates were 0.42 ± 0.01, 0.53 ± 0.03, and 0.10 ± 0.01, for SC18, HP, and STAY, respectively. The genetic correlation estimates were 0.29 ± 0.05, 0.19 ± 0.05, and 0.64 ± 0.07 between SC18 and HP, SC18 and STAY, and HP and STAY, respectively. The residual correlation estimate between HP and STAY was -0.08 ± 0.03. The heritability values indicate the existence of considerable genetic variance for SC18 and HP traits. However, genetic correlations between SC18 and the female reproductive traits analyzed in the present study can only be considered moderate. The small residual correlation between HP and STAY suggests that environmental effects common to both traits are not major. The large heritability estimate for HP and the high genetic correlation between HP and STAY obtained in the present study confirm that EPD for HP can be used to select bulls for the production of precocious, fertile, and long-lived daughters. Moreover, SC18 could be incorporated in multitrait analysis to improve the prediction accuracy for HP genetic merit of young bulls.
对 47605 头大约 18 月龄（SC18）的印度瘤牛公牛的阴囊周长数据与 27924 头小母牛妊娠（HP）和 80831 头可持久配种（STAY）记录进行了同步分析，以估计其加性遗传关系。此外，还验证了通过直接在雌性身上测量具有经济意义的性状是否可以替代 SC18 作为选择标准。小母牛妊娠定义为观察到小母牛受孕并保持妊娠，这是通过在 60 天时直肠触诊来评估的。小母牛第一次接触公牛大约是在 14 月龄（11 至 16 月龄之间）。可持久配种定义为母牛是否每年都产犊，直到 5 岁，当提供繁殖机会时。通过 Gibbs 抽样的贝叶斯线性门限门限分析用于估计多性状模型的方差和协方差分量。SC18、HP 和 STAY 的遗传力估计值分别为 0.42 ± 0.01、0.53 ± 0.03 和 0.10 ± 0.01。SC18 和 HP、SC18 和 STAY 以及 HP 和 STAY 之间的遗传相关估计值分别为 0.29 ± 0.05、0.19 ± 0.05 和 0.64 ± 0.07。HP 和 STAY 之间的剩余相关估计值为-0.08 ± 0.03。遗传力值表明 SC18 和 HP 性状存在相当大的遗传方差。然而，在本研究中分析的 SC18 和雌性生殖性状之间的遗传相关只能被认为是中等的。HP 和 STAY 之间的小剩余相关表明，对两个性状都有共同影响的环境效应不是主要的。本研究中获得的 HP 的高遗传力估计值和 HP 与 STAY 之间的高遗传相关证实，HP 的 EPD 可用于选择生产早熟、肥沃和长寿女儿的公牛。此外，SC18 可以纳入多性状分析中，以提高对年轻公牛 HP 遗传优势的预测准确性。
