Abstract
The main objective of this study was to investigate the impact of adding oregano essential oil (OEO) to adapted and unadapted rumen cultures on methane gas (CH4) production and rumen fermentation under in vitro condition. Rumen fluid for culture fermenters was collected from a Holstein cow located in Southern Illinois University farms.The adapted and unadapted rumen cultures were obtained from continuous culture fermenters fed a control diet, or control diet plus OEO at 250 mg day-1 for 10 days. After 10 days of adaptation, the fermenter’s contents were incubated in a 24 h gas production experiment. Treatments were unadapted culture, unadapted culture plus OEO, adapted culture and adapted culture plus OEO. The OEO was added to rumen cultures at the rate of 500 mg L-1. After 24-h of incubation, total gas production decreased (p<0.03) with the addition of OEO in both cultures and total gas production tended to be lower when added to the adapted cultures. As a percentage of total gas, CH4 production decreased (p<0.05) with OEO addition only in the adapted cultures. Total VFA and acetate concentrations were lower (p<0.05) in the adapted than unadapted cultures and their concentrations decreased (p<0.05) with the addition of OEO, particularly when added to the adapted cultures. Propionate concentrations were also lower (p<0.05) in the adapted than the unadapted cultures and concentrations decreased (p<0.05) with the addition of OEO. The greater effect of OEO on CH4 production in the adapted cultures might have resulted from lower microbial fermentation activity which also might have caused a shift in microbial fermentation favoring less CH4 formation in these cultures.
Highlights
It has been estimated that agricultural activities are responsible for about 10-12% of the total worldwide greenhouse gas emissions and about 50% of methane (CH4) emissions (Smith et al, 2014)
Compared with the control, adding Oregano essential oil (OEO) decreased (p
The addition of OEO reduced (p
Summary
It has been estimated that agricultural activities are responsible for about 10-12% of the total worldwide greenhouse gas emissions and about 50% of methane (CH4) emissions (Smith et al, 2014). In addition to methane gas impact on climate change, it’s considered as an energy loss. Plant extracts and secondary metabolites such as essential oil (EO) were widely evaluated as feed additives to reduce rumen CH4 production due to their antimicrobial properties and negative impact on ruminal microorganisms such as methanogenic Archaea (Benchaar and Greathead, 2011). Oregano essential oil (OEO) contains phenolic monoterpens as thymol and carvacrol known for their strong and broad antimicrobial activity due to the presence of an oxygenated cyclic hydrocarbon in its structure (Helander et al, 1998; Dorman and Deans, 2000; Benchaar and Greathead, 2011)
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