Department of Statistics, Texas A&M University, College Station, TX 7743.
Department of Animal Science, Texas A&M University, College Station, TX 7743.
Front Biosci (Landmark Ed). 2019 Jun 1;24(8):1377-1389. doi: 10.2741/4785.
Amino acid nutrition studies often involve repeated measures data. An example is that the concentrations of plasma citrulline in steers are repeatedly measured from the same animals. The standard repeated measures ANOVA method does not detect significant time changes in the concentrations of plasma citrulline within 6 hours after steers consumed rumen-protected citrulline, while a graphical analysis indicates that there exists a time effect. Here we describe three mixed model analyses that capture the time effect in a statistically significant way, while accounting for the correlations of measurements over time from the same steers. First, we allow flexible variance-covariance structures on our model. Second, we use baseline measurements as a covariate in our model. Third, we use percent-change from baseline as a data normalization method. In our data analysis, all these three approaches can lead to meaningful statistical results that oral administration of rumen-protected citrulline enhances the concentrations of plasma citrulline over time in ruminants. This supports the notion that rumen-protected citrulline can bypass the rumen to effectively enter the blood circulation.
氨基酸营养研究通常涉及重复测量数据。例如，从同一动物中反复测量肉牛血浆瓜氨酸的浓度。标准重复测量方差分析方法未检测到肉牛摄入瘤胃保护瓜氨酸后 6 小时内血浆瓜氨酸浓度的显著时间变化，但图形分析表明存在时间效应。在这里，我们描述了三种混合模型分析方法，这些方法以统计学上显著的方式捕获时间效应，同时考虑了来自同一肉牛的随时间测量的相关性。首先，我们允许模型的方差协方差结构具有灵活性。其次，我们在模型中使用基线测量作为协变量。第三，我们使用从基线的百分比变化作为数据归一化方法。在我们的数据分析中，所有这三种方法都可以得出有意义的统计结果，即口服瘤胃保护瓜氨酸可随时间增强反刍动物血浆瓜氨酸的浓度。这支持了这样一种观点，即瘤胃保护瓜氨酸可以绕过瘤胃，有效地进入血液循环。
