Bohmanova J, Miglior F, Jamrozik J
Department of Animal and Poultry Science, Centre for Genetic Improvement of Livestock, University of Guelph, Guelph, Ontario, Canada.
J Dairy Sci. 2009 Oct;92(10):5314-25. doi: 10.3168/jds.2009-2280.
The Canadian Test-Day Model includes test-day (TD) records from 5 to 305 d in milk (DIM). Because 60% of Canadian Holstein cows have at least one lactation longer than 305 d, a significant number of TD records beyond 305 DIM could be included in the genetic evaluation. The aim of this study was to investigate whether TD records beyond 305 DIM could be useful for estimation of 305-d estimated breeding value (EBV) for milk, fat, and protein yields and somatic cell score. Data were 48,638,184 TD milk, fat, and protein yields and somatic cell scores from the first 3 lactations of 2,826,456 Canadian Holstein cows. All production traits were preadjusted for the effect of pregnancy. Subsets of data were created for variance-component estimation by random sampling of 50 herds. Variance components were estimated using Gibbs sampling. Full data sets were used for estimation of breeding values. Three multiple-trait, multiple-lactation random regression models with TD records up to 305 DIM (M305), 335 DIM (M335), and 365 DIM (M365) were fitted. Two additional models (M305a and M305b) used TD records up to 305 DIM and variance components previously estimated by M335 and M365, respectively. The effects common to all models were fixed effects of herd x test-date and DIM class, fixed regression on DIM nested within region x age x season class, and random regressions for additive genetic and permanent environmental effects. Legendre polynomials of order 6 and 4 were fitted for fixed and random regressions, respectively. Rapid increase of additive genetic and permanent environmental variances at extremes of lactations was observed with all 3 models. The increase of additive genetic and permanent environmental variances was at earlier DIM with M305, resulting in greater variances at 305 DIM with M305 than with M335 and M365. Model M305 had the best ability to predict TD yields from 5 through 305 DIM and less error of prediction of 305-d EBV than M335 and M365. Model M335 had smaller change of 305-d EBV of bulls over the period of 7 yr than did M305 and M365. Model M305a had the least error of prediction and change of 305-d EBV from all models. Therefore, the use of TD records of Holstein cows from 5 through 305 DIM and variance components estimated using records up to 335 DIM is recommended for the Canadian Test-Day Model.
加拿大产奶日模型包含了奶牛产奶5至305天（DIM）期间的产奶日（TD）记录。由于60%的加拿大荷斯坦奶牛至少有一次泌乳期超过305天，因此大量超过305 DIM的TD记录可纳入遗传评估。本研究的目的是调查超过305 DIM的TD记录是否有助于估计牛奶、脂肪、蛋白质产量以及体细胞评分的305天估计育种值（EBV）。数据来自2,826,456头加拿大荷斯坦奶牛前3个泌乳期的48,638,184条TD牛奶、脂肪、蛋白质产量以及体细胞评分记录。所有生产性状均针对妊娠效应进行了预先调整。通过随机抽取50个牛群创建了用于方差成分估计的数据子集。使用吉布斯抽样估计方差成分。完整数据集用于估计育种值。拟合了三个多性状、多泌乳期随机回归模型，其TD记录分别截止到305 DIM（M305）、335 DIM（M335）和365 DIM（M365）。另外两个模型（M305a和M305b）使用截止到305 DIM的TD记录以及先前分别由M335和M365估计的方差成分。所有模型共有的效应包括牛群x产奶日期和DIM类别的固定效应、区域x年龄x季节类别内嵌套的DIM固定回归以及加性遗传和永久环境效应的随机回归。分别对固定回归和随机回归拟合了6阶和4阶勒让德多项式。所有三个模型均观察到泌乳期极端时加性遗传和永久环境方差迅速增加。M305的加性遗传和永久环境方差在较早的DIM时增加，导致M305在305 DIM时的方差大于M335和M365。M305在预测5至305 DIM的TD产量方面能力最佳，且预测305天EBV的误差小于M335和M365。与M305和M365相比，M335在7年期间公牛305天EBV的变化较小。M305a在所有模型中预测误差和305天EBV的变化最小。因此，对于加拿大产奶日模型，建议使用5至305 DIM的荷斯坦奶牛TD记录以及使用截止到335 DIM的记录估计的方差成分。
