Prediction of nitrogen excretion by beef cattle: A meta-analysis1,2,3

• Published in: Journal of animal science 2013-09, Vol.91 (9), p.4290-4302
• Main Authors: Waldrip, H. M., Todd, R. W., Cole, N. A.
• Format: Article
• Language: English
• Subjects: Beef; Meta-analysis; Nitrogen; Predictions; Proteins
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2012-5818

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^sup 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^sup 2^ = 0.003 to 0.14) than N intake (r^sup 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. [PUBLICATION ABSTRACT]