Oscillation of crude protein supply in feedlot Nellore cattle: effects on performance, carcass traits, and nitrogen utilization

This study evaluated five crude protein (CP) supply strategies on performance, carcass traits, nutrient utilization, ruminal fermentation, and nitrogen metabolism in Nellore bulls. Treatments were continuous supply at 100% or 80% of CP requirement, or oscillation between diets at 24-, 48-, or 72-h intervals. In Experiment 1, fifty bulls (380 ± 4.06 kg) received treatments for 98 days. Experiment 2, a 5 × 5 Latin square, assessed ruminal fermentation, nitrogen balance, and plasma metabolites. Oscillating strategies did not differ from continuous 80% CP supply for average daily gain, carcass weight, or dressing percentage (P > 0.05), but average daily gain and carcass weight were lower than with continuous 100% CP supply. Increasing oscillation interval linearly reduced carcass weight, dressing percentage, and subcutaneous fat thickness (P < 0.05). Compared with continuous 100% CP supply, oscillating strategies reduced dry matter intake (13.4 vs. 11.4 kg/d), CP intake (1.53 vs. 1.16 kg/d), and total digestible nutrient intake (9.49 vs. 7.68 kg/d; P < 0.01), whereas CP digestibility increased linearly (P < 0.05). Ruminal pH was unchanged, whereas NH₃–N was lower at 48- and 72-h intervals compared with the 100% CP diet (P = 0.001). Microbial CP synthesis and nitrogen retention efficiency were unaffected, whereas microbial CP synthesis efficiency was greater under oscillating strategies (P < 0.05). Plasma total protein, ALT, and AST were unchanged, whereas plasma urea differed among strategies. O scillating strategies produced performance and carcass traits similar to continuous 80% CP supply, but longer intervals resulted in less favorable responses.