Abstract：
The aim of this study was to estimate the (co)variance components and genetic parameters for milk yield adjusted to 305d (MY305), calving-to-conception interval (CCI), number of services per conception (NSC) and calving interval (CI) of Honduran Holstein cows, by fitting a bivariate animal model using Maximum Restricted Likelihood procedures. Model included the fixed effects of calving number, the contemporary calving group (farm-season-year of calving and the cow age as covariate). The estimated means and standard deviations for MY, CCI, NSC and CI were, 5098.60 ± 1564.32 kg, 168.27 ± 104.71 days, 2.46 ± 1.69 services, and 448.73 ± 109.16 days, respectively; and their estimated heritabilities were 0.21 ± 0.05, 0.03 ± 0.028, 0.02 ± 0.024 and 0.06 ± 0.04, respectively. The genetic correlations between MY305 and CCI, NSC and CI were positive and antagonist, with values of 0.64 ± 0.52, 0.99 ± 0.56, and 0.32 ± 0.24 respectively. Even though moderate to low heritability was estimated for MY305, systematic selection for milk yield, with a reduction in reproductive efficiency, if considered as the only selection criterion is important to be considered. By including reproductive traits and considering permanent environment effects into the breeding program, might yield a slow, but constant and permanent improvement over time.
摘要：
这项研究的目的是估计调整为305d（MY305）的牛奶产量的（协）方差成分和遗传参数，产卵到受孕间隔(CCI)，洪都拉斯荷斯坦奶牛的每次受孕服务数量(NSC)和产卵间隔(CI)，通过使用最大限制似然程序拟合双变量动物模型。模型包括产仔数的固定效应，当代产牛群体(农场季节产牛年和母牛年龄为协变量)。MY的估计平均值和标准偏差，CCI、NSC和CI是，5098.60±1564.32kg,168.27±104.71天,2.46±1.69服务，448.73±109.16天，分别为0.21±0.05、0.03±0.028、0.02±0.024和0.06±0.04。MY305与CCI，NSC和CI之间的遗传相关性为阳性和拮抗剂，值分别为0.64±0.52、0.99±0.56和0.32±0.24。尽管MY305的遗传力估计为中等至低，但对产奶量的系统选择，随着生殖效率的降低，如果被认为是唯一的选择标准，那么需要考虑的是重要的。通过将繁殖特性和永久环境影响纳入育种计划，可能会产生缓慢的，但随着时间的推移不断和永久的改善。
