Prediction of urinary and fecal nitrogen excretion by beef cattle.
Dong, R.L., Zhao, G.Y., Chai, L.L., and Beauchemin, K.A. (2014). "Prediction of urinary and fecal nitrogen excretion by beef cattle.", Journal of Animal Science, 92(10), pp. 4669-4681. doi : 10.2527/jas.2014-8000 Access to full text
An analysis of predicting urinary and fecal N excretion from beef cattle was conducted using a data set summarizing 49 published studies representing 180 treatment means for 869 animals. Variables included in the data set were initial BW (kg), DMI (kg/d), dietary CP content (% of DM), N intake (g/d), apparent total tract N digestibility (%), and urinary and fecal N excretion (g/d). Correlation analysis examined relationships between animal and dietary variables and N excretion. A mixed model regression analysis was used to develop equations to predict N excretion in urine and feces and the proportion of urinary N in total N excretion as a function of various animal and dietary variables. Of the single animal and dietary variables, N intake was the best predictor of N excretion in urine and feces, whereas apparent total tract N digestibility was best to predict the proportion of urinary N in total N excretion. Low prediction errors and evaluation of the equations using cross-validation indicated the prediction equations were accurate and robust. Urinary and fecal N excretion can be accurately and precisely predicted by N intake, whereas the proportion of urinary N in total N excretion was best predicted solely using apparent total tract N digestibility.
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