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United States Department of Agriculture

Agricultural Research Service

Title: The Effects of Dietary Crude Protein Concentration on Nitrogen Absorption and Retention by Feedlot Steers

Authors
item Gueye, A. - TEXAS TECH
item Richardson, C. - TEXAS TECH
item Mikus, J. - TEXAS TECH
item Nunnery, G. - TEXAS TECH
item Cole, Noel
item Greene, L. - TAES

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2003
Publication Date: June 22, 2003
Citation: Gueye, A., Richardson, C. R., Mikus, J. H., Nunnery, G. A., Cole, N. A., Greene, L. W. The Effects of Dietary Crude Protein Concentration on Nitrogen Absorption and Retention by Feedlot Steers. Journal of Animal Science. 2003. v. 81(Suppl.1). p. 110. Abstract No. M129.

Technical Abstract: Twenty seven crossbred steers (average BW = 353.2 ± 8.4 kg) were used in a metabolism trial with three collection periods (approximately 35, 95, and 155 d on feed) to evaluate the effects of dietary CP source and concentration on nitrogen balance by steers. Treatments were arranged in a factorial design and consisted of three dietary CP concentrations (11.5, 13.0, and 14.5%) and three supplemental urea:cottonseed meal (CSM) ratios (100:0, 50:50, and 0:100 of supplemental N). During each nutrient collection period steers were housed in individual metabolism stalls and urine and feces excreted were collected and frozen. Collection periods consisted of a 2- to 5-d adaptation period followed by a 5-d collection period. On d 35 on feed, total N excretion increased linearly (P = 0.002) with increasing CP concentration. Nitrogen absorbed (g/d) and N retained (g/d)linearly increased (P < 0.0001 and P = 0.01, respectively) with increasing CP concentration. On d 95 on feed, total N excretion linearly increased (P < 0.0001) with increasing CP concentration. Nitrogen absorbed (g/d) and N retained linearly increased (P < 0.0001 and P = 0.001, respectively) when CP increased from 11.5 to 14.5%. On d 155 on feed, DM digestibility decreased linearly (P < 0.05) with increasing dietary CP. Fecal N excretion increased linearly (P < 0.0001) with increasing CP. Nitrogen absorbed (g/d) decreased linearly (P = 0.03) with decreasing urea:CSM ratio. Nitrogen absorbed (% of intake) increased quadratically (P = 0.05) with decreasing urea:CSM ratio. As days on feed increased, total N excretion also increased (P < 0.02). Based on our observations, feeding growing steers diets containing 11.5 to 13.0% CP and supplemented with higher proportions of degradable protein may potentially optimize N utilization and potentially reduces N losses to the environment.

Last Modified: 9/22/2014
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