Influence of oscillating dietary crude protein concentration on performance, acid-base balance, and nitrogen excretion of steers1,2,3

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 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.

The influence of oscillating dietary protein concentrations on finishing cattle. II. Nutrient retention and ammonia emissions

“…Previous studies showed that oscillation of the dietary CP improved N retention of ruminants (Collins and Pritchard, 1992;Cole, 1999;Cole et al, 2003). This improvement in the retention of N may provide a viable means to reduce the release of N, especially ammonia, into the environment.…”

Need for protein supplementation in the diet of growing dairy bulls fed total mixed ration based on moderate digestible grass silage and barley

“…Klopfenstein and Erickson 2002). Decreasing dietary protein inputs in feeding could potentially decrease environmental concerns related to air and water quality (Cole et al 2003). Increased P excretion should be avoided by using mineral feeds of low P content together with these by-products.…”

Evaluation of protein supplementation for growing cattle fed grass silage-based diets: a meta-analysis

“…Decreasing dietary protein inputs in diet could potentially decrease environmental impacts related to air and water quality (Cole et al, 2003). The P content in some protein supplements, especially in RSM, is high compared with the basal diet based on forages and grains (MTT, 2014).…”