Influence of oscillating dietary crude protein concentration on performance, acid-base balance, and nitrogen excretion of steers

• Published in: Journal of animal science Vol. 81; no. 11; pp. 2660 - 2668
• Main Authors: Cole, N.A, Greene, L.W, McCollum, F.T, Montgomery, T, McBride, K
• Format: Journal Article
• Language: English
• Published: Savoy, IL Am Soc Animal Sci 01.11.2003; American Society of Animal Science
• Subjects: acid-base balance; Acid-Base Equilibrium; Animal Feed; animal nutrition; Animal productions; Animals; backfat; beef carcasses; Biological and medical sciences; Blood Gas Analysis - veterinary; blood plasma; Body Composition - drug effects; carcass characteristics; Cattle - growth & development; Cattle - metabolism; cattle manure; crude protein; dietary protein; Dietary Proteins - administration & dosage; Dietary Proteins - metabolism; Dose-Response Relationship, Drug; excretion; feces; Feces - chemistry; Fundamental and applied biological sciences. Psychology; Male; metabolites; nitrogen; Nitrogen - metabolism; Nitrogen - urine; Nutritional Requirements; Random Allocation; steers; Terrestrial animal productions; urine; Vertebrates; Weight Gain - drug effects; Performance evaluation; Excretion; Farming animal; Nutrition; Ruminant animal; Animal feeding; Nitrogen; Experimental study; Weight gain; Protein; Acid base balance; Acid-Base Balance; Vertebrata; Mammalia; Steers; Concentration effect; Beef cattle; Artiodactyla; Crude protein; Ungulata; Protein content
• ISSN: 1525-3163; 0021-8812; 1525-3163
• DOI: 10.2527/2003.81112660x

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 thereby 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. Steers were fed to a constant backfat thickness in both studies. In the first trial, 92 steers (mean BW = 408 ± 2.8 kg; four pens/treatment) were fed the following diets: 1) constant 12% CP, 2) constant 14% CP, and 3) 10 and 14% CP oscillated at 2-d intervals. Steer performance and carcass characteristics were measured. In the second trial, 27 steers were individually fed the same three experimental dietary regimens (nine 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 (P < 0.10) to have greater 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 = 0.09) 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 = 0.04) for steers fed the 14% CP diet than steers fed the 12% CP diet. Steers fed the oscillating CP regimen tended (P = 0.08) to have greater calculated protein retention (g/d) than steers fed the 12% CP diet. Steers fed the 14% CP diet had greater (P < 0.05) calculated urinary N excretion than steers fed the 12% CP or oscillating CP regimens. Venous plasma concentrations of urea N were greater (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 CP 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 CP requirement was greater than 6.3% of diet DM. However, the effects of oscillating dietary CP were minimal.