Invited Review: Essential Oils as Modifiers of Rumen Microbial Fermentation

Metabolic pathways of the biosynthesis of the main plant extract active components.

The main monoterpenoid (A), sesquiterpenoid (B), and phenylpropanoid (C) components of essential oils.

Hypothesized mechanism of action of carvacrol in the cytoplasmic membrane (Ultee et al., 2002). The undissociated carvacrol diffuses through the cytoplasmic membrane toward the cytoplasm and dissociates, thereby releasing its proton to the cytoplasm. Later, undissociated carvacrol returns by carrying a potassium ion (or another ion) from the cytoplasm to the extracellular medium. Carvacrol liberates this ion in the extracellular medium and recovers an additional hydrogen to close the cycle.

Percentage change and standard error in total VFA (TVFA), acetate (C₂), and propionate (C₃) caused by the incubation of rumen fluid of beef steers fed a 10 to 90 straw-to-concentrate diet at pH 7.0 (■) or pH 5.5 (□) in the presence of capsicum or cinnamaldehyde compared with a control. (Adapted from Cardozo et al., 2005.)