Reaction norm model with unknown environmental covariate to analyze heterosis by environment interaction.
Reaction norm model with unknown environmental covariate to analyze heterosis by environment interaction.
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DOI：
10.3168/jds.2008-1499
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发表时间：
2009-05
影响因子：
3.5
通讯作者：
G. Su;P. Madsen;M. Lund
中科院分区：
文献类型：
--
作者：
G. Su;P. Madsen;M. Lund
目前奶牛生产中的杂交育种正在增加。一些研究显示了环境依赖性杂种优势[即杂种优势与环境之间的相互作用(H x E)]。 H x E 相互作用通常是根据几个离散的环境级别来估计的。本研究提出了一种反应范数模型来描述 H x E 相互作用，该模型可以使用很少的参数处理大量的环境水平。在所提出的模型中，总杂种优势由与环境无关的部分（被描述为杂合性的函数）和环境依赖的部分（被描述为杂合性和环境价值的函数（例如牧群年效应））组成。开发了贝叶斯方法来同时估计线性和非线性反应范数中的环境协变量、反应范数的回归系数以及模型的其他参数。在非线性反应范数模型中，H x E 使用线性样条进行近似。该方法使用模拟数据进行了测试，这些数据是使用具有杂种优势反应标准的动物模型生成的。模拟研究包括非线性形式的 H x E 相互作用的 4 种情景（中度与低度遗传力和中度与低度牧群年份变异的组合）。在所有情况下，所提出的模型都很好地预测了总杂种优势。在牧群年份变异较低的情况下，真实杂种优势与预测杂种优势之间的相关性为0.98，在牧群年份变异中等的情况下，真实杂种优势与预测杂种优势之间的相关性为0.99。这表明所提出的模型和方法可能是分析 H x E 相互作用并预测杂种优势在环境梯度上逐渐且连续变化的情况下的育种值的好方法。另一方面，我们发现，在环境依赖性杂种优势效应的方差很小（通常如此）并且在生产环境中随机使用种公牛的模拟情景下，忽略 H x E 相互作用的模型不会显着损害育种价值的预测。
Crossbreeding is currently increasing in dairy cattle production. Several studies have shown an environment-dependent heterosis [i.e., an interaction between heterosis and environment (H x E)]. An H x E interaction is usually estimated from a few discrete environment levels. The present study proposes a reaction norm model to describe H x E interaction, which can deal with a large number of environment levels using few parameters. In the proposed model, total heterosis consists of an environment-independent part, which is described as a function of heterozygosity, and an environment-dependent part, which is described as a function of heterozygosity and environmental value (e.g., herd-year effect). A Bayesian approach is developed to estimate the environmental covariates, the regression coefficients of the reaction norm, and other parameters of the model simultaneously in both linear and nonlinear reaction norms. In the nonlinear reaction norm model, the H x E is approximated using linear splines. The approach was tested using simulated data, which were generated using an animal model with a reaction norm for heterosis. The simulation study includes 4 scenarios (the combinations of moderate vs. low heritability and moderate vs. low herd-year variation) of H x E interaction in a nonlinear form. In all scenarios, the proposed model predicted total heterosis very well. The correlation between true heterosis and predicted heterosis was 0.98 in the scenarios with low herd-year variation and 0.99 in the scenarios with moderate herd-year variation. This suggests that the proposed model and method could be a good approach to analyze H x E interactions and predict breeding values in situations in which heterosis changes gradually and continuously over an environmental gradient. On the other hand, it was found that a model ignoring H x E interaction did not significantly harm the prediction of breeding value under the simulated scenarios in which the variance for environment-dependent heterosis effects was small (as it generally is), and sires were randomly used over production environments.