PSXI-20 Nitrogen use efficiency is affected by protein source in feedlot Nellore steers fed high-concentrate diets

Abstract

Abstract Nitrogen use efficiency (NUE) has implications for production performance, economic efficiency and for the emission of contaminants to the environment. Thus, the objective of this study was to evaluate whether high-concentrate diets with different levels (10 and 13% crude protein) and protein source can affect the NUE and nitrogen (N) excretion. The protein sources tested were urea, dried distillers grains (DDG) and corn gluten meal. Our hypothesis is that reducing the level of N in the diet associated with the use of rumen undegradable protein (RUP) could increase the NUE in high-concentrate diets. The hypotheses were tested using 6 cannulated Nellore steers, rumen, duodenum and ileum arranged in 6×6 Latin square designed in factorial (2 nitrogen levels and 3 protein sources) balanced for residues. The concentration of N in samples was analyzed using the Dumas combustion method. The statistical analysis was performed using the MIXED procedure of the statistical package SAS. The N intake and retention was not affected by level and protein source (P > 0.05). Fecal N excretion was not affected by the levels and protein sources tested (P > 0.05). However, there was effect of protein source (P < 0.001) and tendency to protein level in the diet (P < 0.10) on urinary N excretion. In the treatments containing the urea source, there was an increase in the urinary N excretion (46.8 g.dia-1) compared to the Gluten and DDG sources with 28.8 and 27.0 g of N excreted in the urine per day, respectively. The NUE was affected by the protein source (P < 0.05). Diets containing urea had lower NUE (31.8%) compared to corn gluten meal and DDG sources with NUE of 40.3 and 41.2%, respectively. Using RUP (DDG or Gluten) in high-concentrate diets can be a nutritional strategy for increase NUE and this response is partly attributable to decreased urinary N excretion.