Abstract #339

# 339
Effects of supplementation to steers consuming green chopped wheat pasture on energy losses and nitrogen balance.
Adam L. Shreck*1, Pake J. Ebert3, Eric A. Bailey3, Jenny S. Jennings2, Ken D. Casey2, N. Andy Cole1, 1USDA-ARS, Bushland, TX, 2Texas Agrilife Research, Amarillo, TX, 3West Texas A&M University, Canyon, TX.

British cross steers (n = 10; initial BW: 206 ± 10.7 kg) were studied using respiration calorimetry chambers to evaluate energy losses, N balance, and nutrient digestibility of greenchop wheat forage as affected by energy supplementation. The study was designed as a 2 × 2 factorial arrangement of treatments. Eight steers were assigned to one of 2 BW blocks (4 steers per block) with factors consisting of either dietary treatment [no supplementation (CON) vs. supplemented with a corn-based energy supplement that contained 150 mg monensin sodium per steer/daily) at 0.5% of BW daily (SUP)] and NEm intake level [(1-times (1×) vs. 1.5-times (1.5×) maintenance]. Wheat forage was harvested daily and fed as green chop to steers continuously during the 56-d study. No difference (P ≥ 0.29) was observed between CON and SUP for apparent digestibility of OM (79.6% vs. 79.6%), NDF (68.7% vs. 64.7%), or N (82.2% vs. 80.4%). No difference was observed for DE (2.90 Mcal/kg), heat production (8.54 vs. 8.29 Mcal), or retained energy (4.98 vs. 4.06 Mcal) between dietary treatments when fed at 1.5× maintenance. CON steers had greater (P = 0.01) O2 consumption (1,790 vs. 1,711 L/d), tended to have (P = 0.06) greater CH4 production (78 vs. 65 L/d), and had similar CO2 production (1,704 vs. 1,627 L/d; P = 0.62) compared with SUP. Methane, as a proportion of GE intake, was 6.50% and 6.00%, for CON and SUP, respectively, but was not significantly different (P = 0.60) between treatments. No difference (P = 0.69) was noted in retained energy as a proportion of GE intake (24.8 vs. 23.0%) between treatments. We determined that the CON treatment (wheat forage alone) contained 1.61 Mcal/kg NEm and 0.98 Mcal/kg NEg and the SUP treatment contained 1.78 Mcal/ kg NEm and 0.95 Mcal/kg NEg. By difference, supplementation improved the calculated NEm of wheat forage by 10.6% but decreased NEg of wheat forage by 3.1%. Under the conditions of this study, supplementation of wheat forage with a corn-based supplement did not affect losses of energy and resulted in similar NE values.

Key Words: methane, net energy, wheat forage