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United States Department of Agriculture

Agricultural Research Service

Title: Influence of Oscillating Dietary Crude Protein Concentration on Performance, Acid-Base Balance, and Nitrogen Excretion of Steers

Authors
item Cole, Noel
item Greene, L. - TAES
item Mccollum, F. - TCE
item Montgomery, T. - WTAMU
item Mcbride, K. - TAES / TEXAS TECH

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 5, 2003
Publication Date: November 1, 2003
Citation: Cole, N.A., Greene, L.W., Mccollum, F.T., Montgomery, T., Mcbride, K. 2003. Influence of oscillating dietary crude protein concentration on performance, acid-base balance, and nitrogen excretion of steers. Journal Of Animal Science. 72:2660-2668.

Interpretive Summary: Decreasing dietary nitrogen inputs into beef cattle feeding operations could potentially decrease environmental concerns relating to air and water quality. Ruminants have the unique ability to recycle nitrogen from the lower gut to the rumen, thus improving the efficiency of protein utilization. In an attempt to take greater advantage of nitrogen recycling, we conducted two studies to determine the effects of oscillating dietary crude protein (CP) concentrations on performance (weight gain, feed use efficiency), acid-base balance, and manure characteristics of steers fed high-concentrate finishing diets. In both trials, steers fed a 14% CP diet tended to have better average daily gains and feed efficiencies than steers fed a 12% CP diet. Steers fed the oscillating CP regimen (10 and 14% CP at 48-hour intervals) had intermediate performance. Steers fed the oscillating CP regimen tended to have greater calculated protein retention (g/d) than steers fed the 12% CP diet. Venus plasma concentrations of urea nitrogen were higher in steers fed the 14% CP diet than in steers fed the 12% CP diet; steers fed the oscillating CP regimen were intermediate but concentrations fluctuated over days. Based on arterial blood gas concentrations, acid-base balance was not affected by dietary regimen. Results of these trials suggest that the CP requirement of steers in these studies was greater than 12% of the diet dry matter and/or that the degradable protein requirement was greater than 6.3% of diet DM. However, the effects of oscillating dietary CP were minimal.

Technical Abstract: Decreasing dietary N inputs into beef cattle feeding operations could potentially decrease environmental concerns relating to air and water quality. Previous studies with sheep suggest that oscillating dietary CP concentrations may improve N use efficiency and thus decrease dietary N requirements. Therefore, two studies were conducted to determine the effects of oscillating dietary CP concentrations on performance, acid-base balance, and manure characteristics of steers fed high-concentrate diets to a constant backfat thickness. In the first trial 92 steers (mean BW 408 + 2.8 kg: 4 pens/treatment) were fed the following diets: 1) constant 12% CP, 2) constant 14% CP, 3) 10 and 14% CP oscillated at 2-day intervals. Steer performance and carcass characteristics were measured. In the second trial, 27 steers were individually fed the same three experimental dietary regimens (9 steers/treatment). Animal performance, arterial acid-base balance, plasma metabolites, and fecal characteristics were measured. In both trials steers fed the 14% CP diet tended to have greater (P < 0.10) ADG and gain:feed than steers fed the 12% CP diet. Steers fed the oscillating CP regimen had intermediate performance. In trial 1 steers fed, the 14% CP diet tended (P < 0.10) to have smaller longissimus area and higher quality grades than steers fed the oscillating CP regimen. Protein retentions (g/d) calculated from NRC (2000) equations were greater (P < 0.05) for steers fed the 14% CP diet than steers fed the 12% CP diet. Steers fed the oscillating CP regimen tended (P < 0.10) to have greater calculated protein retention (g/d) than steers fed the 12% CP diet. Steers fed the 14% CP diet had greater calculated urinary N excretion than steers fed the 12% CP or oscillating CP regimens. Venus plasma concentrations of urea N were higher (P < 0.001) in steers fed the 14% CP diet than in steers fed the 12% CP diet; steers fed the oscillating CP regimen were intermediate but fluctuated over days. Based on arterial blood gas concentrations, acid-base balance was not significantly affected by dietary regimen. Results of these trials suggest that the CP requirement of steers in these studies was greater than 12% of the diet DM and/or that the degradable protein requirement was greater than 6.3% of diet DM. However, the effects of oscillating dietary CP were minimal.

Last Modified: 9/23/2014
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