Effect of Mootral and Forage Amount on Methane Emission, Growth and Carcass Characteristics of Feedlot Steers

Methane (CH₄) production from enteric fermentation in ruminant animals is a contributor to global greenhouse gas emissions. Because CH₄ has an impact on increasing global temperatures, there is a push for government regulations to reduce CH₄ from livestock animals. At 1.9% of U.S. CH₄ emissions beef cattle are a large contributor to agricultural CH₄ emissions or (EPA, 2020). Enteric CH₄ emissions are also a loss of energy for the animal, accounting for 2-12% of energy loss from the ruminant animal (Johnson & Johnson, 1995). This energy loss from the diet is contingent upon forage content, where increasing forages in the diet increases CH₄ yield (g/kg of gross energy intake; van Gastelen et al., 2019). Mootral is a feed supplement that contains garlic (Allium sativum) and bitter orange (Citrus aurantium) extracts. The organosulfur compounds in garlic the flavonoids found in bitter orange extracts are known to decrease CH₄ production, (Busquet et al., 2005a; Balcells et al., 2012; Seradj et al., 2014). However, it is unclear how the forage content and Mootral inclusion will interact to effect CH₄ production and animal performance. Because feedlot cattle are fed a range of forage:concentrate ratios while in the feedlot, it is important to know how effective mitigation strategies are in different forage:concentrate diets. Therefore, the objective of the current study was to quantify CH₄ production and determine growth, intake, and carcass characteristics of feedlot steers fed Mootral in diets with a low, medium, and high forage content. Knowing the effect of garlic and flavonoids on methanogenesis, we hypothesized that Mootral would decrease CH₄ emissions without impacting growth, intake, and carcass characteristics of feedlot steers. We expect that the CH₄ mitigating ability of Mootral will be greatest in the diet with the most forage. For the experiment, 144 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 42-46 and day 203-207. Data were analyzed using the GLIMMIX procedure of SAS. There was an interaction (P = 0.03) between forage content 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 content or Mootral on BW or average daily gain at any time, or on DMI from d 84 to slaughter and overall. 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 15 or 41.5% corn silage. On d 42-46, steers fed 41.5 and 68% corn silage had increased (P ≤ 0.02) methane emissions compared to steers fed 15% corn silage. Mootral did not affect methane emissions on day 42-46 (P ≥ 0.47), but there was a forage effect, where steers fed the 41.5 and 68% corn silage diets 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. Steers fed Mootral emitted less (P ≤ 0.03) methane on a g/d, g/kg DMI, and g/kg BW basis on d 203-207 compared to steers not fed Mootral. Mootral tended to decrease (P ≤ 0.09) fat thickness and yield grade. In conclusion, increasing forage content increased methane emissions and Mootral decreased methane production in 15% corn silage diets and improved carcass leanness.