Crude protein requirements of large frame cattle fed two levels of energy as weaned calves or as backgrounded yearlings

Abstract

Two trials were conducted to determine the crude protein (CP) requirements of large-frame (LF) cattle managed under two regimes and fed one of two energy levels. Trial 1 involved 216 recently weaned LF calves, while trial 2 involved 192 LF backgrounded yearling steers. In each trial, the cattle were fed diets formulated to one of two energy levels (11.17 and 11.88 MJ ME kg−1 DM) and one of six CP levels (11, 13, 15, 16, 17 and 19% DM basis). High-energy feeding increased (P < 0.05), average daily gain (ADG), average daily carcass gain (ADCG) and average daily fat gain (ADFG) of weaned calves but did not influence the performance of the backgrounded yearlings. Weaned calves fed 16, 17 or 19% CP had higher (P < 0.05) ADG than those fed 11%, while those fed 16% CP exhibited increased (P < 0.05) ADFG. ADG and ADCG of weaned calves and backgrounded yearlings and ADFG of weaned calves fed low-energy diets increased (P < 0.05) linearly with increasing dietary CP concentration. Daily carcass lean gain of weaned calves fed low-energy diets decreased in a quadratic manner (P < 0.05) as dietary CP level increased. No influence of dietary CP concentration was observed on carcass tissue gain of the backgrounded yearlings. It was concluded that energy balance of animals fed low-energy diets improved with CP supplementation and that current NAS-NRC (1984) CP requirements accurately predict performance of LF cattle. Key words: Steers, growth, carcass composition, energy, crude protein