Effects of dietary crude protein and supplemental urea levels on nitrogen and phosphorus utilization by feedlot cattle

J. T. Vasconcelos, N. A. Cole, K. W. McBride, A. Gueye, M. L. Galyean, C. R. Richardson, L. W. Greene

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Three dietary CP concentrations (11.5, 13.0, and 14.5% of DM) and 3 supplemental urea levels (100, 50, and 0% of supplemental N) were used in a completely randomized block design experiment conducted at 2 locations to determine N and P balance and serum urea N (SUN) concentrations of feedlot cattle. Crossbred steers [British and British × Continental; initial BW = 315.0 ± 3.2 kg at location 1 (n = 27) and initial BW = 353.2 ± 8.4 kg at location 2 (n = 27)] were used in 3 nutrient balance sampling periods (SP) at the beginning, middle, and end of the feeding period (154 d in location 1 and 159 d in location 2). Fecal N (g/d; P = 0.03), urinary N (g/d; P < 0.01), urinary urea N (UUN; g/d; P < 0.01), apparent N absorption (g/d; P < 0.01), and SUN concentration (mg/dL; P < 0.01) increased linearly as dietary CP concentration increased. Nitrogen retention (g/d) was not affected (P = 0.61) by dietary CP concentration. Phosphorus intake (g/d; P = 0.02), fecal P (g/d; P = 0.04), and urinary P (g/d; P = 0.01) increased linearly as dietary CP increased, reflecting changes in diet composition with increasing CP concentrations. As dietary urea levels increased, urinary N (g/d; P = 0.04), UUN (g/d; P = 0.01), and apparent N absorption (g/d; P = 0.04) increased linearly, but P intake (g/d; P= 0.10) and urinary P (g/d; P = 0.02) decreased linearly. No interactions were observed between SP and dietary treatments for most variables. Evaluation of SP means, however, showed that as days on feed increased, fecal N (g/d; P = 0.01), urinary N (g/d; P < 0.01), UUN (g/d; P < 0.01), apparent absorption of N (g/d; P < 0.01), SUN (mg/dL; P < 0.01), and urinary P (g/d; P < 0.01) increased linearly, whereas retained N (g/d) decreased linearly (P < 0.01) with increasing days on feed. These data suggest that changes in dietary CP and urea levels, as well as stage of the feeding period, markedly alter N and P utilization by feedlot cattle.

Original languageEnglish
Pages (from-to)1174-1183
Number of pages10
JournalJournal of animal science
Issue number3
StatePublished - Mar 2009


  • Beef cattle
  • Crude protein
  • Feedlot
  • Nitrogen
  • Phosphorus
  • Urea


Dive into the research topics of 'Effects of dietary crude protein and supplemental urea levels on nitrogen and phosphorus utilization by feedlot cattle'. Together they form a unique fingerprint.

Cite this