LAUSR

One hundred and forty-four Angus x Simmental steers were allotted by body weight (BW; 363 kg), breed composition, and farm origin to a 3 x 2 factorial arrangement of 6 treatments (4 pens per treatment) to determine the effect of Mootral (garlic + citrus extract; 0.25% of the diet DM vs. 0.0%) on methane emissions, growth and carcass characteristics of feedlot cattle. During the first 84 days, cattle were fed three different forage concentrations in the diet (15, 41.5, or 68% corn silage) with or without Mootral. From day 85 to slaughter, corn silage was included at 15% of the diet DM with or without Mootral. Methane emissions were measured on day 42 to 46 and day 203 to 207. Data were analyzed using the GLIMMIX procedure of SAS. Mootral did not affect methane emissions on days 42 to 46 (P ≥ 0.47), but there was a forage effect, where steers fed the 68% corn silage emitted more methane on a g/d (P = 0.05) and a g/kg of DMI (P = 0.007) basis and tended (P = 0.07) to produce more methane on g/kg BW basis compared to steers fed the 15% corn silage diet. On d 203 to 207, steers fed Mootral emitted less (P ≤ 0.03) methane on a g/d, g/kg DMI, and g/kg BW basis compared to steers not fed Mootral. There was an interaction (P = 0.03) between forage concentration and Mootral for DMI from d 0 to 84, where Mootral decreased DMI of steers fed 15% corn silage but did not affect DMI of steers fed 41.5 or 68% corn silage. There were no effects (P ≥ 0.22) of forage concentration or Mootral on BW or average daily gain at any time, or on DMI from d 84 to slaughter and overall. However, overall calculated NEm and NEg tended to be greater for steers fed Mootral (P ≤ 0.10). Intake from d 0-84 was lower and gain:feed from d 0-84 and overall was greater (P = 0.04) for steers fed 68% compared to steers fed 41.5% corn silage. Calculated NEm and NEg from day 0 to 84 and overall were greater for steers fed 68% corn silage compared to steers fed 41.5% corn silage (P ≤ 0.03). Mootral tended to decrease (P ≤ 0.09) fat thickness and yield grade. In conclusion, increasing forage concentration increased methane emissions and Mootral decreased methane production in 15% corn silage diets and tended to improve carcass leanness.