MEASUREMENT OF GREENHOUSE GAS EMISSIONS FROM BEEF CATTLE USING THE GREENFEED SYSTEM

Production of air pollutants by beef cattle operations has incurred increased scrutiny in recent years. Two experiments quantified gaseous emissions of beef cattle in a feedlot and while grazing wheat pasture. In experiment 1, the effects of supplementing a finishing diet (14.4% CP; 1.47 Mcal/kg NEg) for beef steers with a commercially-available condensed tannin extract (CT) at three levels (0, 0.5, and 1.0 % of diet, DM basis) were evaluated. Angus-cross steers (n = 27; initial BW = 350 + 32 kg) were fed individually via Calan gates for 126 d. Ruminal methane (CH4) and metabolic carbon dioxide (CO2) fluxes were measured using a GreenFeed system (GF, C-Lock Inc., Rapid City, SD) for two sampling periods, that coincided with fecal and urine sampling.. Oxygen consumption was estimated from CO2 production assuming a respiratory quotient of 1.05. Average daily gain (2.08, 2.14, and 2.08 kg/d for 0, 0.5, and 1.0% CT, respectively) and G:F did not differ (P = 0.88) among treatments. Apparent total tract starch digestibility during phase 1 decreased (P = 0.01) with inclusion of 1% CT. Fecal N excretion was greater (P = 0.05) for 1.0% CT during phase 1. Urinary N excretion was not different (P ≥ 0.39) among treatments during both phases, but urinary N as a proportion of total N excretion decreased (P = 0.01) when CT was included in the diet during phase 1. No differences (P ≥ 0.23) were observed for percentage of GE intake lost as CH4 (phase 1: 2.99, 3.12, 3.09%; phase 2: 3.54, 3.55, and 4.35%) for 0, 0.5, and 1.0%
CT, respectively. In experiment 2, effects of concentrate supplementation of steers grazing wheat forage were evaluated. Thirteen Angus-cross steers (initial BW = 436 + 24 kg) were used in a crossover design to evaluate the effects of corn supplementation on gas emissions, performance, and energetic losses of steers grazing wheat pasture. Treatments included either 0.2 kg of pelleted wheat middlings (CON), or a dry-rolled corn supplement fed at 0.5% of BW plus 0.2 kg of pelleted wheat middlings (SUPP). Forage intake was calculated using the determined fecal output and estimated forage digestibility. Ruminal CH4 and CO2 fluxes were measured using a GreenFeed system. Urine energy loss was assumed to be 1.4% of GE intake. Oxygen consumption was estimated from CO2 production, assuming a respiratory quotient of 1.05. Fecal output was estimated using TiO2 as an external marker. Forage intake as percent of BW did not differ (P = 0.15) between CON (3.22%) and SUPP (3.61%). Corn supplementation decreased (P = 0.02) CH4 g/kg of DMI by 20.5%. Methane as percent of GE intake was decreased (P = 0.02) by 21.6% when steers consumed SUPP. Supplementation of condensed tannins in a feedlot or concentrate grazing production setting appears to alter emissions of air pollutants without affecting performance. However, more research is warranted to evaluate the varying levels of supplementation and interactions with various diets.