Wiggans G R, Misztal I, Van Tassell C P
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350.
J Dairy Sci. 2003 May;86(5):1845-8. doi: 10.3168/jds.S0022-0302(03)73771-0.
Variance components for a sire-maternal grandsire (MGS) threshold model were estimated from subsets of the US calving ease (CE) database, which includes over 10 million calving records with CE scored 1 (no problem) to 5 (extreme difficulty). Selected records included sire and MGS among the 2601 most frequently appearing bulls. The data were further restricted by requiring at least 20 records in each herd year. Five mutually exclusive sample datasets of approximately 200,000 records each were created based on herd code. The model included random herd-year, sire, MGS, and residual effects and fixed year-season, parity-sex, and birth year of sire and MGS effects. Fewer than 50 iterations were required to reach convergence. The (co)variance component estimates from the five replicates were quite similar. The set of estimates (0.438, herd-year; 0.022, sire; 0.016, MGS; 0.009, sire-MGS) that yielded among the highest heritabilities (0.086, direct; 0.048, maternal) and a correlation of direct and maternal effects near the mean (-0.12) was selected for use in the implementation of a sire-MGS model for CE.
从美国产犊难易度（CE）数据库的子集中估计了父系-母系祖父（MGS）阈值模型的方差分量，该数据库包含超过1000万条产犊记录，CE评分从1（无问题）到5（极度困难）。选定的记录包括2601头出现频率最高的公牛中的父系和MGS。通过要求每个畜群年份至少有20条记录，数据进一步受限。基于畜群代码创建了五个相互排斥的样本数据集，每个数据集约有200,000条记录。该模型包括随机畜群年份、父系、MGS和残差效应，以及固定的年份季节、胎次-性别和父系与MGS的出生年份效应。达到收敛所需的迭代次数少于50次。五个重复估计的（协）方差分量非常相似。选择了一组估计值（0.438，畜群年份；0.022，父系；0.016，MGS；0.009，父系-MGS），这些估计值产生了最高的遗传力（0.086，直接；0.048，母体）以及直接和母体效应之间接近平均值的相关性（-0.12），用于实施CE的父系-MGS模型。
