Garlic as a rumen modifier for eco-friendly and economic livestock production

Allium sativum (garlic) has been very popular in Asian kitchen as one of the major spices. The strong smelling juice of bulb contains volatile oils composed of sulphur-containing compounds: allicin, diallyl disulfide and diallyl trisulfide, which are responsible for anti-microbial activity. Recently garlic, its oil, extracts in different organic and aqueous solvents and individual components of essential oils have been examined as a feed additive to manipulate rumen function for controlling enteric methane emission and improving feed conversion efficiency. The results reported so far indicate that garlic and its essential oils inhibit methanogenesis significantly accompanied with a lower acetate to propionate ratio indicating a diversion of fermentation in a favourable direction. As methanogenesis is the major hydrogen sink in the rumen, its inhibition requires the disposal of reducing equivalents produced during fermentation of feed. The propionate synthesis serves as an alternate hydrogen sink. The anti-microbial compounds present in garlic appear to be selective inhibitors of methanogenesis, as there is no adverse effect on feed degradation in the rumen. Garlic and its oil adversely affect the protein degrading bacteria and deamination activity of the rumen contents. Only a few in vivo experiments have been conducted using garlic as a feed additive, and it appears to have good potential for rumen manipulation for eco-friendly (with minimum methane emission) and economic livestock production.