Effect of Dietary Protein Levels and Growth Promotants in Dairy-Beef Cross Steers on Nitrogen Utilization Efficiency

Abstract Reducing nitrogen excretion of finishing beef cattle is needed to protect the environment but methods used to decrease nitrogen excretion need to have economic benefits as well. The objective of this experiment was to determine the potential of implant strategy and phase-feeding crude protein (CP) to reduce urinary nitrogen (UN) and fecal nitrogen excretion. Holstein × Angus steers (n = 72) were blocked by body weight (BW) and treatments were randomly assigned to pens (n = 4 per treatment). This experiment was a 2 × 2 factorial design, where cattle were fed a constant CP (control), or the CP content of the diet was reduced every 49 days (phase-fed) and cattle received either an aggressive or moderate implant strategy. All cattle were implanted on d-0 and d-98. Body weight was measured, and blood, urine, and fecal samples were collected on days 0, 49, 98, 147, and at shipping. Phase-feeding CP and implant strategy had no effect (P ≥ 0.47) on dry matter intake or average daily gain. There was a tendency (P = 0.10) for a diet × implant-strategy interaction for feed efficiency, indicating that phase-fed cattle were more efficient with the moderate implant strategy than the aggressive implant strategy. UN excretions decreased (P < 0.01), on day-147 among both implant treatments, indicating that re-implanting on d-98 may have reduced nitrogen excretion. There was a sampling-day × implant interaction (P ≤ 0.03) and a sampling-day × diet interaction (P < 0.01) for blood urea nitrogen concentrations (BUN) and total UN excretion, where BUN and total UN excretion were decreased among the moderate implant and the phase-fed groups on day-147 compared with the aggressive implant and control-fed groups, respectively. Overall, fecal nitrogen concentrations were less for the phase-fed treatment group compared with the control (P ≤ 0.05). These results suggest that phase-feeding CP can be an effective strategy to reduce nitrogen excretion from cattle in the feedlot without negatively affecting performance.