Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, Bellaterra, Spain.
Genet Sel Evol. 2010 Feb 25;42(1):6. doi: 10.1186/1297-9686-42-6.
A procedure to measure connectedness among herds was applied to a beef cattle population bred by natural service. It consists of two steps: (a) computing coefficients of determination (CDs) of comparisons among herds; and (b) building sets of connected herds.
The CDs of comparisons among herds were calculated using a sampling-based method that estimates empirical variances of true and predicted breeding values from a simulated n-sample. Once the CD matrix was estimated, a clustering method that can handle a large number of comparisons was applied to build compact clusters of connected herds of the Bruna dels Pirineus beef cattle. Since in this breed, natural service is predominant and there are almost no links with reference sires, to estimate CDs, an animal model was used taking into consideration all pedigree information and, especially, the connections with dams. A sensitivity analysis was performed to contrast single-trait sire and animal model evaluations with different heritabilities, multiple-trait animal model evaluations with different degrees of genetic correlations and models with maternal effects.
Using a sire model, the percentage of connected herds was very low even for highly heritable traits whereas with an animal model, most of the herds of the breed were well connected and high CD values were obtained among them, especially for highly heritable traits (the mean of average CD per herd was 0.535 for a simulated heritability of 0.40). For the lowly heritable traits, the average CD increased from 0.310 in the single-trait evaluation to 0.319 and 0.354 in the multi-trait evaluation with moderate and high genetic correlations, respectively. In models with maternal effects, the average CD per herd for the direct effects was similar to that from single-trait evaluations. For the maternal effects, the average CD per herd increased if the maternal effects had a high genetic correlation with the direct effects, but the percentage of connected herds for maternal effects was very low, less than 12%.
The degree of connectedness in a bovine population bred by natural service mating, such as Bruna del Pirineus beef cattle, measured as the CD of comparisons among herds, is high. It is possible to define a pool of animals for which estimated breeding values can be compared after an across-herds genetic evaluation, especially for highly heritable traits.
应用于自然交配的肉牛群体的一种衡量关联度的方法，包括两个步骤：（a）计算牛群之间比较的决定系数（CD）；（b）建立连接牛群的集合。
使用基于抽样的方法计算牛群之间的 CD，该方法从模拟的 n 个样本中估计真实和预测育种值的经验方差。一旦估计了 CD 矩阵，就应用一种可以处理大量比较的聚类方法来构建 Bruna dels Pirineus 肉牛的紧密连接的牛群集群。由于在这个品种中，自然交配占主导地位，与参考种牛几乎没有联系，因此为了估计 CD，使用了一种动物模型，该模型考虑了所有系谱信息，特别是与母畜的联系。进行了敏感性分析，以对比不同遗传力的单一性状种牛和动物模型评估、不同遗传相关性的多性状动物模型评估以及具有母本效应的模型。
使用种牛模型，即使对于高度遗传的性状，连接牛群的比例也非常低，而使用动物模型，该品种的大多数牛群都很好地连接在一起，并且在它们之间获得了高 CD 值，尤其是对于高度遗传的性状（模拟遗传力为 0.40 时，每个牛群的平均 CD 的平均值为 0.535）。对于遗传力较低的性状，平均 CD 从单一性状评估的 0.310 增加到中度和高度遗传相关性的多性状评估的 0.319 和 0.354。在具有母本效应的模型中，直接效应的每个牛群的平均 CD 与单一性状评估相似。对于母本效应，如果母本效应与直接效应具有高遗传相关性，则每个牛群的平均 CD 会增加，但母本效应的连接牛群比例非常低，低于 12%。
如 Bruna del Pirineus 肉牛，通过自然交配繁殖的牛群的关联程度（衡量为牛群之间比较的 CD）很高。可以定义一组动物，在进行跨牛群遗传评估后，可以比较它们的估计育种值，尤其是对于高度遗传的性状。
