The effect of Origanum syriacum L. extract and carvacrol on the in vitro digestion, estimated digestion values, ammonia and organic acid concentrations in the fermentation fluid of lucerne herbage

The effects induced by medicinal aromatic plants in biological systems vary with the type and amount of bioactive substances these plants contain. Whether the purified form of the main chemical components of these plants, such as carvacrol and thymol, or plant volatile oils containing tens of bioactive compounds are more effective remains a question of debate. This study was aimed at providing a comparative assessment of the effects of Origanum syriacum L. (wild mountain thyme) volatile oil (OSVO) and one of its main components, carvacrol (CRV), on the in vitro ruminal degradability of lucerne herbage and methane production during the degradation of lucerne. For this purpose, wild thyme was harvested at the beginning of the flowering period, and the OSVO was extracted from the plant by steam distillation. Gas production assays were performed in five groups of ruminal fluid samples, one of which was maintained for control purposes, and the other four 40/60/80 mg/l of OSVO and 60 mg/l of CRV were added. Compared to the control group, in the samples with the added CRV and OSVO, the amounts of in vitro total gas and methane production were observed to have been affected, but no decrease was detected in the ruminal protozoa counts. The level of ammonia nitrogen was lowest in the groups, in which CRV and 40 mg/l of OSVO (P < 0.01) were added. The ruminal protozoa counts were not affected by the addition of CRV and OSVO. While the total volatile fatty acid (TVFA) and propionic acid (PA) concentrations in the in vitro fermentation fluid of lucerne herbage were low in all the groups, butyric acid was detected at a level of 40 mg/l in the group where CRV was added. The OSVO was ascertained to have induced dose-dependent alterations in the investigated in vitro digestion parameters. In result, CRV (60 mg/l) and OSVO (40 mg/l) were determined to have shown a relatively positive effect on the in vitro ruminal gas production. The anti-methanogenic effect of the plant extracts was due to the decreased digestibility of the lucerne herbage. This can have a positive impact on the environment, but the same cannot be said for the animal nutrient use and animal performance.