Effect of different levels of citrus essential oil and its active component on rumen microbial fermentation and methane production in vitro

Sobhy M. A. Sallam, Samir A. M. Abdelgaleil


The fermentation characteristics of adding different levels (0, 25, 50 and 75 ?L/75mL buffered rumen fluid) of citrus essential oil or its
bioactive component (limonene, 0, 30, 45 and 60 ?L/75mL buffered rumen fluid) to a basal substrate (50% roughage: 50% concentrate) were evaluated in vitro by semi automatic gas production (GP) technique. The investigated essential oil was Citrus reticulata (CR25, CR50, CR75), and Limonene (L30, L45, L60). The analyses of the citrus essential oils by GC/MS showed that the main components were dl-Limonene (83.9 %) and ?- Terpinene (10.75 %) There were significant differences (P < 0.05) in cumulative gas production (GP) after subtracting the blank gas volume for different levels of citrus essential oil or limonene. All levels of citrus essential oil and limonene were significantly (P < 0.05) decreased the GP in compare to the substrate without additive. The second and third dose of citrus essential oil or limonene decreased (P < 0.05) methane emission when expressed on dry matter basis, but when expressed on the base of digested organic matter the third dose only from citrus essential oil decreased (P < 0.05) methane emission in vitro. The inhibition of methane production was along with a significant reduction in protozoa count. Partitioning factor (PF) was used as an index of the efficiency of microbial protein synthesis in vitro. There was no significant effect of citrus essential oils on PF, while limonene supplementation declined (P < 0.05) the PF values. The inclusion of citrus essential oil or limonene was affected negatively on true digestibility of dry and organic matter. The NH3-N concentration was dramatically declined with inclusion of high level of citrus or limonene. This study suggested that the citrus essential oil has the potential to affect ruminal fermentation efficiency and could be a promising methane mitigating agent, which attributed to its rich content of limonene.
Key words: citrus, limonene, essential oil, gas production, methane, protozoa, degradation.

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