An energy supplement with monensin reduces methane emission intensity of stocker cattle grazing winter wheat

Objective: The objective of this study was to determine the effect of an energy supplement with monensin on CH4 emissions and performance of stocker calves grazing winter wheat. Materials and Methods: Eight steers and 8 heifers were grazed in a 9-ha winter wheat pasture, and CH4 emissions were recorded. Animals were randomly assigned within sex to receive from 0 to 1.07 kg of a supplement (as fed, primarily ground corn, wheat middlings, and 34 mg/kg monensin) per day. Animals were supplemented 3 d per week in individual stalls and orts were weighed. Forage intake was estimated with TiO2 as an external marker. As several independent variables were available, dependent variables of interest were subjected to backward stepwise regression with baseline CH4, total supplement intake, forage intake, initial BW, sex, and monensin dose in the model. Results and Discussion: Animal performance increased, but at a decreasing rate, with increased total supplement intake and forage intake (P < 0.02; R-2 = 0.47). Supplement intake reduced forage intake (P < 0.01; R-2 = 0.77) with initial BW and sex in the model. Methane emissions increased with increasing forage intake and initial BW, but heifers produced less CH4 than steers (P < 0.01; R-2 = 0.74). Increasing supplement intake reduced CH4 emission intensity (g of CH4/kg of BW gain; P = 0.03) when baseline CH4 was included in the model. Implications and Applications: Taken together, these results suggest that supplementation with energy and monensin likely reduces methane emission intensity, and provide equations useful for future modeling efforts.