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

Abstract

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.

Effect of Garlic Straw with Silage Corn Stalks on Hu Sheep Rumen Fermentation and Microbial Community In Vitro

“…Its relative feeding value resembles silage maize, establishing it as an excellent unconventional roughage [25]. This study further demonstrated that including 60% garlic straw significantly enhanced dry matter digestibility, aligning with prior research [19,26].…”

“…The incorporation of garlic straw impacts various indicators, with gas production as a pivotal measure of rumen fermentation activity, providing insight into the action of rumen microorganisms. While previous research indicated that substances derived from garlic, such as garlic leaf [14], garlic powder [15][16][17], garlic oil [18], allicin [19], and other extracts were able to reduce methane production, our study yielded consistent results in the G80 group. Specifically, the addition of silage garlic straw led to an increase in the rumen gas production in Hu sheep.…”

“…However, there is no consensus on how garlic and its by-products influence rumen VFA. For instance, studies have shown that garlic oil had no significant effect on the total concentration of VFAs [18,19]. On the other hand, allicin has been reported to enhance total short-chain fatty acid (SCFA) engagement, organic matter (OM), and fiber digestibility in sheep.…”

Inclusion of molasses to garlic foliage silage and its effect on <i>in vitro</i> ruminal fermentation and gas production

“…Thus, T1 which contained the highest concentration of garlic foliage (i.e. also sulphur compounds), was expected to show a higher antiprotozoal activity, and in consequence, lower methanogenesis due to reduced transfer of hydrogens, as detailed earlier (Sari et al, 2022). On the other hand, if garlic foliage and methanogenesis suppressors were reduced, a higher protozoal activity should be expected, and indeed it was observed in T4.…”

Therapeutic Potential of Garlic (Allium sativum) in Ruminants

“…The digestive system of ruminants mainly comprises the rumen, reticulum, omasum, and abomasum (Sari et al, 2022). Rumen is the most important and largest chamber that harbors a large number of microorganisms (Paswan et al, 2022).…”