Dietary Strategies for Mitigation of Methane Production by Growing and Finishing Cattle

Three experiments were conducted to evaluate the effects of diet and monensin on performance, digestibility, and methane production in steers fed forage-based diets. In Exp. 1, 72 individually fed steers (300 ± 25 kg) were used in a randomized block design arranged as 2 separate 2 × 2 factorials with two common treatments, thus 6 diets were fed with 12 steers per treatment. Factors included high (HQ) or low (LQ) quality forage with 0 or 200 mg/steer daily of monensin. An additional two HQ diets with 0% modified distillers grain plus solubles (MDGS) were fed with or without monensin to create another 2 × 2 factorial of 0 or 40% MDGS and monensin. Calan gate bunks were partially enclosed and outfitted with a small air pump that was used to gradually fill a gas collection bag at time of feeding. In diets containing 40% MDGS, monensin in a LQ diet tended to decrease DMI (forage x monensin interaction; P = 0.06) and ADG (P = 0.08), but had no impact on performance in HQ diets (P > 0.05). A forage x monensin interaction was observed for CH4:CO2 and for L of CH4 produced per day and per kg of DMI (P < 0.05) where monensin decreased CH4 in LQ, however no effect was observed in HQ diets. In Exp. 2, 6 crossbred steers (369 ± 17 kg) were used in a 3-period switchback calorimetry study to evaluate CH4 production by steers fed HQ or LQ forage with 20% MDGS. Intake of DM, OM, and ADF were greater for cattle fed HQ forage compared to LQ forage (P ≤ 0.01). Apparent total tract digestibility of DM tended (P = 0.08) to be greater for those cattle fed HQ forage compared to LQ forage. Methane and CO2 production (L/d) were also greater (P < 0.01) for cattle fed HQ forage. In Exp. 3, 60 individually fed steers (310 ± 28 kg) were used in a randomized block design with 6 treatments: 4 diets containing differing forages (cornstalks, sorghum silage, husklage, and