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

Abstract

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.

Nutrient Requirements of Zebu and Crossbred Cattle - BR-CORTE

“…Predictions of N excretion proposed by Waldrip et al (2013) and Dong et al (2014), and used by BCNRM (2016), also showed a positive correlation between nitrogen intake and excretion. These authors observed better fit of the prediction equations using the N intake than the percentage of crude protein in the diet, and the same behavior was observed in the present database.…”

“…Prior to generating new equations for nitrogen and phosphorus excretion, prediction equations of nitrogen and phosphorus excreted (Geisert et al, 2010;Waldrip et al, 2013;Dong et al, 2014) as proposed by BCNRM (2016), were tested for appropriateness for these database. The tested equations are presented below.…”

“…Urinary N (g/d) = -21.18 + 0.56 × NI [Waldrip et al, 2013] Fecal N (g/d) = 24.28 + 0.15 × NI [Waldrip et al, 2013] Urinary N (g/d) = -14.12 + 0.51 × NI [Dong et al, 2014] Fecal N (g/d) = 15.82 + 0.20 × NI [Dong et al, 2014] Urinary N (g/d) = 2.39 + 0.55 × NI -3.36 × DMI [BCNRM, 2016] Total P (g/d) = 0.82 + 0.57 × P intake [Geisert et al, 2010] where NI is nitrogen intake (g/d); DMI is dry matter intake (kg/d) and P intake is phosphorus intake (g/d). The equations proposed by BCNRM (2016) were tested using the BR-CORTE (2016) database.…”

“…The equations for nitrogen excretion (Waldrip et al, 2013;Dong et al, 2014) use nitrogen intake as an independent variable. The BCNRM (2016) proposed an equation for predicting urinary N excreted using the nitrogen intake and dry matter intake as independent variables.…”

Aumento das doses dietéticas de líquido de casca de castanha de caju na digestibilidade ruminal e intestinal de nutrientes em novilhos alimentados com uma dieta rica em grãos

“…Titanium dioxide concentration was determined in samples of duodenal digesta and feces according Myers et al (2004) to determine intestinal and total solids flow. (Waldrip et al, 2013).…”