Garlic and Its Bioactive Compounds: Implications for Methane Emissions and Ruminant Nutrition

Simple Summary Methane (CH4) produced by ruminants contributes as a source of anthropogenic greenhouse gases (GHG). Plant-derived bioactive compounds have been investigated for their potential to reduce CH4 emissions from ruminant livestock. Garlic contains bioactive organosulphur compounds, which have been reported to be effective in reducing CH4 emissions, but they have demonstrated inconsistent effects in reducing CH4 production in the rumen. This might be because different types of garlic-based supplements vary in their concentrations of bioactive compounds. Therefore, further investigation is needed, such as the mode of action and persistence of the bioactive compound, to determine whether these compounds can be used successfully to inhibit rumen methanogenesis. The present review discusses garlic and its potential contribution to reducing CH4 production by ruminant animals and discusses how differences in the diet and the concentration of bioactive compounds in garlic might contribute to inconsistent CH4 mitigation potential of garlic. Methane (CH4) emission from enteric fermentation of ruminant livestock is a source of greenhouse gases (GHG) and has become a significant concern for global warming. Enteric methane emission is also associated with poor feed efficiency. Therefore, research has focused on identifying dietary mitigation strategies to decrease CH4 emissions from ruminants. In recent years, plant-derived bioactive compounds have been investigated for their potential to reduce CH4 emissions from ruminant livestock. The organosulphur compounds of garlic have been observed to decrease CH4 emission and increase propionate concentration in anaerobic fermentations (in vitro) and in the rumen (in vivo). However, the mode of action of CH4 reduction is not completely clear, and the response in vivo is inconsistent. It might be affected by variations in the concentration and effect of individual substances in garlic. The composition of the diet that is being fed to the animal may also contribute to these differences. This review provides a summary of the effect of garlic and its bioactive compounds on CH4 emissions by ruminants. Additionally, this review aims to provide insight into garlic and its bioactive compounds in terms of enteric CH4 mitigation efficacy, consistency in afficacy, possible mode of action, and safety deriving data from both in vivo and in vitro studies.

Automated summary

Garlic's organosulphur compounds have been found to decrease methane emissions and increase propionate concentration in the rumen, but the mode of action and consistency of these effects are not fully understood. The effectiveness of garlic-based supplements may vary due to differences in the concentration and impact of individual substances. Further research is needed to determine the potential of garlic in inhibiting rumen methane production.