USDA-ARS, Conservation and Production Research Laboratory, P.O. Drawer 10, Bushland, TX 79012, USA.
J Anim Sci. 2013 Sep;91(9):4290-302. doi: 10.2527/jas.2012-5818. Epub 2013 Jul 3.
Reliable estimates of N excretion in the urine and feces of beef cattle are essential for developing cost-effective and environmentally sound nutrient management plans. A meta-analysis dataset was compiled that included data for starting live BW, DMI, N intake, dietary CP and RDP concentrations, urine N excretion, and feces N excretion. The data were taken from 12 individual feeding trials that included N balance data, and represented a total of 47 different dietary treatments and 255 animals. Correlation analysis was used to determine the animal and dietary parameters that were most closely related to N excretion in urine and feces by beef cattle. A multivariate mixed modeling approach was used to develop empirical equations to predict excretion of urine N, feces N, and the partitioning of total N excretion between urine and feces, as a function of N intake and the concentration of dietary CP. Univariate, regression, and mean difference comparisons indicated 46 to 95% agreement between observed and predicted values for the developed equations. Evaluation of the equations with an independent dataset taken from 6 studies, and 2 random subsets of the meta-analysis dataset showed moderate agreement (P < 0.05, r(2) = 0.34 to 0.86) for urine N excretion as a function of both N intake and %CP, and the partitioning of total N excretion into urine as a function of %CP. There was less agreement between predictions and observations for feces N excretion as a function of %CP (r(2) = 0.003 to 0.14) than N intake (r(2) = 0.52 to 0.75), indicating that %CP is not a good predictor of fecal N excretion. The empirical equations provide a simple tool that, if used with caution, could predict N excretion characteristics for a wide range of dietary and animal characteristics and could improve ammonia emissions estimates by process-based models.
可靠估计肉牛尿液和粪便中的氮排泄量对于制定具有成本效益和环境友好的养分管理计划至关重要。本研究汇编了一个包含启动活体重、干物质采食量、氮摄入量、日粮 CP 和 RDP 浓度、尿液氮排泄量和粪便氮排泄量的元分析数据集。这些数据来自 12 个单独的饲养试验，其中包括氮平衡数据，共代表了 47 种不同的日粮处理和 255 头动物。通过相关分析确定了与肉牛尿液和粪便氮排泄最密切相关的动物和日粮参数。采用多元混合模型方法，建立了预测氮摄入量和日粮 CP 浓度对尿液氮、粪便氮和总氮排泄在尿液和粪便中分配的经验方程。单变量、回归和平均差异比较表明，所开发方程的观测值与预测值之间的一致性为 46%至 95%。用来自 6 项研究的独立数据集和元分析数据集的 2 个随机子集对方程进行评估表明，氮摄入量和 CP%对尿液氮排泄的影响以及 CP%对总氮排泄在尿液中的分配的影响，方程具有中等一致性（P＜0.05，r2=0.34 至 0.86）。CP%对粪便氮排泄的预测值与观测值之间的一致性较差（r2=0.003 至 0.14），而氮摄入量的一致性较好（r2=0.52 至 0.75），表明 CP%不是粪便氮排泄的良好预测因子。经验方程提供了一种简单的工具，如果谨慎使用，它可以预测广泛的日粮和动物特性下的氮排泄特征，并可以通过基于过程的模型改善氨排放估计。
