Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, USP, Ribeirão Preto, SP, Brazil.
J Anim Breed Genet. 2012 Feb;129(1):20-9. doi: 10.1111/j.1439-0388.2011.00934.x. Epub 2011 May 31.
Validity of comparisons between expected breeding values obtained from best linear unbiased prediction procedures in genetic evaluations is dependent on genetic connectedness among herds. Different cattle breeding programmes have their own particular features that distinguish their database structure and can affect connectedness. Thus, the evolution of these programmes can also alter the connectedness measures. This study analysed the evolution of the genetic connectedness measures among Brazilian Nelore cattle herds from 1999 to 2008, using the French Criterion of Admission to the group of Connected Herds (CACO) method, based on coefficients of determination (CD) of contrasts. Genetic connectedness levels were analysed by using simple and multiple regression analyses on herd descriptors to understand their relationship and their temporal trends from the 1999-2003 to the 2004-2008 period. The results showed a high level of genetic connectedness, with CACO estimates higher than 0.4 for the majority of them. Evaluation of the last 5-year period showed only a small increase in average CACO measures compared with the first 5 years, from 0.77 to 0.80. The percentage of herds with CACO estimates lower than 0.7 decreased from 27.5% in the first period to 16.2% in the last one. The connectedness measures were correlated with percentage of progeny from connecting sires, and the artificial insemination spread among Brazilian herds in recent years. But changes in connectedness levels were shown to be more complex, and their complete explanation cannot consider only herd descriptors. They involve more comprehensive changes in the relationship matrix, which can be only fully expressed by the CD of contrasts.
从最佳线性无偏预测程序获得的预期育种值在遗传评估中的比较有效性取决于牛群之间的遗传关联性。不同的牛种培育计划有其自身的特点，这些特点区分了其数据库结构，并可能影响关联性。因此，这些计划的演变也会改变关联性度量。本研究使用基于对比确定系数（CD）的法国准入集团关联牛群标准（CACO）方法，分析了 1999 年至 2008 年巴西内罗尔牛群的遗传关联性度量的演变。通过对牛群描述符进行简单和多元回归分析，研究了遗传关联性水平，以了解它们之间的关系及其在 1999-2003 年至 2004-2008 年期间的时间趋势。结果表明，遗传关联性水平较高，大多数 CACO 估计值高于 0.4。对最后 5 年的评估显示，与前 5 年相比，平均 CACO 指标仅略有增加，从 0.77 增加到 0.80。CACO 估计值低于 0.7 的牛群比例从第一阶段的 27.5%下降到最后一个阶段的 16.2%。关联性度量与来自关联种公牛的后代比例相关，以及近年来巴西牛群中的人工授精传播。但是，关联性水平的变化更为复杂，其完整解释不能仅考虑牛群描述符。它们涉及到关系矩阵的更全面变化，只能通过对比确定系数充分表达。
