Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 1/17/2003
Publication Date: 3/17/2003
Citation: Mcbride, K. W., Greene, L. W., Cole, N. A., McCollum, F. T., Galyean, M. L. Nitrogen And Phosphorus Utilization By Beef Cattle Fed Three Dietary Crude Protein Levels With Three Levels Of Supplemental Urea. Available from: http://www.Asas.Org/Midwest/2003/03mabs.pdf. Midwestern Section of the American Society of Animal Science. No. 291.  Interpretive Summary:
Technical Abstract: Three dietary CP levels (11.5, 13.0, and 14.5\% of DM) and three supplemental urea levels (100, 50, and 0\% of supplemental CP from urea) were fed to determine performance, serum urea N (SUN), and N and P balance. Crossbred steers (n = 27; average BW = 315 kg) were blocked by weight and individually fed the nine treatments in a completely randomized block design. A steam flaked corn-based diet was fed, with supplemental CP supplied by either all urea, a 50:50 blend of urea and cottonseed meal (CSM), or all CSM. Steers were used in three nutrient balance collection periods (NBCP) at the beginning, middle, and end, of the feeding period. Venous jugular blood was obtained at the start and end of each NBCP. No CP level x CP source interactions (P < 0.10) were observed. Steer DMI, ADG, and feed efficiency did not differ (P < 0.05) among treatments. For each NBCP, urinary total N, urinary urea N (UUN), and SUN increased linearly (P < 0.10) as CP level increased. For NBCP 1 and 3, fecal N output increased linearly (P < 0.10) as supplemental CP from urea decreased. For NBCP 2 and 3, UUN decreased linearly (P < 0.10) as urea level decreased. For NBCP 1, fecal and urine P excretion increased linearly (P < 0.10), and P retained (% of intake) decreased linearly (P < 0.10), as CP level increased. Phosphorus intake increased linearly (P < 0.10) as urea level decreased for each NBCP. Fecal P output increased linearly (P < 0.10) in all NBCP, and urinary P excretion in NBCP 1 and 2 increased linearly (P < 0.10) as urea level decreased. Phosphorus retained (% of intake) decreased linearly (P < 0.10) as urea level decreased for NBCP 3. Results suggest that as dietary CP level increased, N retention decreased, and as supplemental CP supplied by urea decreased P balance decreased in feedlot steers. As days on feed increased, less N and P were retained, suggesting the potential to decrease N and P excretion by feeding less N and P as the feeding period progresses.