Potential of Nutritional Strategies to Reduce Enteric Methane Emission in Feedlot Sheep: A Meta-analysis and Multivariate Analysis

The objective of this study was to use meta-analytical methods to evaluate the effects of nutritional strategies on the reduction of enteric methane emission in feedlot sheep. Additionally, this study aimed to evaluate interrelationships among diet composition, intake and digestibility of nutrients, rumen parameters, rumen microbial population, nitrogen metabolism and enteric methane production in sheep. The dataset was composed by 45 peer-reviewed publications with 102 treatment means. The strategies to mitigate enteric methane emission were evaluated by examining the weighted mean difference between control treatment (diets containing no additives and/or any other strategies to mitigate methane emission) and reduced-methane treatment (diets containing strategies to mitigate methane emission: protozoa-free, nitrate, lipids, saponins, essential oils and tannins). The interaction of factors associated with diet composition, nutrient intake and digestibility, rumen parameters on methane emission from sheep depends on how methane production is expressed (Production=CH4 g/d vs Yield= CH4 g/kg DMI). Lipids inclusion to diets reduced methane production in 6.28 g/d and 5.87 g CH4/kg of DMI. Oil inclusion in amounts greater than 20 g oil/day reduced methane production (CH4 g/d). Lipid inclusion to diets presented the greatest effectiveness in reducing methane emission in sheep fed TMR diets containing different forage: concentrate ratios. Tannins inclusion to diets reduced methane production in 1.22 g/d CH4 and 2.61 gCH4/kg of DMI, presenting long-term effect on methane emission. Tannins effects on methane production were greater in sheep fed high-forage total mixed rations. Rumen defaunation (protozoa-free) and essential oils inclusion to diets had no effects on methane production. Although methane production reduced with saponin and nitrate inclusion to diets, further studies are needed to confirm their effects on methane emission and better elucidate factors interacting with the response of sheep to saponins and nitrate supplementation.