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1665
WS Effect of corn-based supplementation on gas emissions, performance, and energetic losses of steers grazing wheat pasture
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. Steers were allowed ad libitum access to wheat pasture (1.2 steers/ha), and were individually supplemented one of two treatments daily for two 30 d periods. 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). After initial 30 d period, treatments were alternated and steers were supplemented an additional 30 d. Fecal output was determined with titanium dioxide (TiO2)as an external marker. Beginning on d 14 of each period 15 g of TiO2 was added to each steers supplement. In vitro analysis of wheat forage was determined to estimate DM digestibility of the wheat forage for each 30 d period. Forage intake was calculated using the determined fecal output and estimated forage digestibility. Ruminal CH4 and CO2 fluxes were measured using a GreenFeed (C-Lock Inc., Rapid City, SD) system. Urine energy loss was assumed to be 1.4% of GE intake. Oxygen production was estimated from CO2 production, assuming a respiratory quotient of 1.05. Forage intake as percent of BW did not differ (P = 0.15) between CON (3.22%) and SUPP (3.61%). Average daily gain for CON and the SUPP averaged 1.4 kg and 1.3 kg, respectively, and was not influenced (P = 0.54) by supplementation. There were no differences (P ≥ 0.63) among treatments for OM digestibility (CON: 84.9%; SUPP: 84.6%) and NDF digestibility (CON: 82.5%; SUPP: 83.1%). Carbon dioxide excreted (CON: 9.8 kg/d; SUPP: 10.5 kg/d) tended to be less (P = 0.08) for CON. No differences (P = 0.43) were observed in CH4 emissions among CON and the SUPP supplement (334 and 351 g CH4/d, respectively). 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 the SUPP compared to CON. Heat production as a percent of GE intake decreased (P = 0.03) when steers consumed the SUPP. Under the conditions of this experiment, cereal grain supplementation reduced CH4 emissions.
Keywords: methane, wheat pasture, energetic losses