207 Effects of increasing dietary metabolizable protein in lightweight beef calves

Abstract

Abstract The objective was to assess the effect of increasing metabolizable protein (MP) supply to lightweight beef steers on total tract digestion, N balance, and performance. The 2016 Beef Cattle Nutrient Requirements Model (BCNRM) prediction of MP requirements in lightweight beef steers (less than 250 kg) is limited by available data. Spring-born Angus steers (n = 12; BW = 166 +/- 10.7 kg) were weaned at 97 ± 10 d of age, backgrounded 42 d, implanted with Component TE-IS, stratified by BW, and assigned to one of four treatments in a crossover design with two 19 day periods. Each period included a 12-day adaptation followed by a 6-day collection period of total orts, feces, and urine. Treatment diets were formulated to provide 0.62 (MP1), 0.76 (MP2), 0.89 (MP3), and 1.01 (MP4) kg MP per day. Metabolizable energy was similar across diets (2.14 Mcal/kg). Data were analyzed using the Mixed procedure of SAS. Dry matter intake was not affected by treatment (P = 0.92) and averaged 5.7 kg per d. Average daily gain (ADG) tended (P = 0.06) to increase quadratically with MP provision with 1.45, 1.72, 1.93, and 1.71 kg per day for MP1, MP2 MP3, and MP4, respectively. Feed efficiency (G:F) also increased quadratically (P = 0.05) at 0.27, 0.32, 0.35, and 0.31 for MP1, MP2 MP3, and MP4, respectively. Greater dietary MP linearly increased (P < 0.01) N intake, N absorption, and urinary N. Fecal N and retained N were not affected by treatment (P ≥ 0.56). Apparent organic matter digestibility increased linearly (P ≤ 0.01). Increasing MP resulted in a linear increase in N absorption but a quadratic response for ADG, suggesting MP greater than 0.89 kg per d may exceed MP requirements for steers weighing 166 kg and consuming a 2.14 Mcal/kg diet.