Caraviello D Z, Weigel K A, Gianola D
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
J Dairy Sci. 2004 Aug;87(8):2677-86. doi: 10.3168/jds.S0022-0302(04)73394-9.
Survival analysis with a Weibull proportional hazards model was used to evaluate the effects of 15 linear type traits, 5 composite traits, and final score on the functional longevity of US Holstein cows. Culling data and type classification scores (measured in first lactation) from 891,524 cows with first calving from 1993 to 2000 were used. The data were divided into 9 geographical regions to determine whether the relationship between type traits and longevity differed according to climate or management system. Functional survival was defined as the number of days from first calving until culling or censoring, after correction for 305-d mature equivalent combined fat and protein yield. The Weibull model included time-dependent effects of herd-year-season, parity-stage of lactation, and within herd-year quintile ranking for combined fat and protein yield (nested within biennium), as well as time-independent effects of age at first calving and type classification score (type traits were analyzed one at a time). Type classification scores were rounded to the nearest 5 points, and the impact of each type trait on functional survival in each region was evaluated. Mean failure time ranged from 694 d in the South to 758 d in the North East. Risk of culling differed by region for several linear type traits, and differences were greatest for regions that were most dissimilar in climate and herd management (e.g., South East, East North Central, and West). Udder depth, fore udder attachment, udder cleft, and rear legs side view were consistently associated with functional longevity, regardless of region, but, the importance of some secondary traits, such as stature or dairy form, differed by region. The survival model applied in this study easily described both linear and nonlinear relationships between type traits and longevity while accounting for important time-dependent and time-independent explanatory variables.
采用威布尔比例风险模型进行生存分析，以评估15个线性类型性状、5个复合性状和最终得分对美国荷斯坦奶牛功能寿命的影响。使用了1993年至2000年首次产犊的891,524头奶牛的淘汰数据和类型分类评分（首次泌乳时测量）。数据被分为9个地理区域，以确定类型性状与寿命之间的关系是否因气候或管理系统而异。功能存活被定义为从首次产犊到淘汰或截尾的天数，校正305天成熟当量的脂肪和蛋白质总产量后得到。威布尔模型包括畜群-年份-季节的时间依赖性效应、胎次-泌乳阶段以及畜群-年份五分位数排名（嵌套在两年期内）对脂肪和蛋白质总产量的影响，以及首次产犊年龄和类型分类评分的时间独立性效应（类型性状一次分析一个）。类型分类评分四舍五入到最接近的5分，并评估每个类型性状对每个区域功能存活的影响。平均失效时间从南部的694天到东北部的758天不等。几个线性类型性状的淘汰风险因区域而异，气候和畜群管理差异最大的区域差异最大（例如，东南部、东北中部和西部）。无论区域如何，乳房深度、前乳房附着、乳房裂和后腿侧视图始终与功能寿命相关，但一些次要性状（如体高或乳用体型）的重要性因区域而异。本研究中应用的生存模型在考虑重要的时间依赖性和时间独立性解释变量的同时，轻松描述了类型性状与寿命之间的线性和非线性关系。
