In vitro evaluation of the effects of Lavandula officinalis and Origanum vulgare essential oils on ruminal fermentation using concentrate and roughage type substrates

The aim of this research was to study the in vitro effect of Lavandula officinalis (LEO) and Origanum vulgare (OEO) essential oils on rumen fermentation using a concentrate type substrate (CTS) and roughage type substrate (RTS). Six Mehraban ewes were divided into 2 groups and fed a concentrate type or roughage type diet, and used as rumen fluid donors. Each essential oil (EO) was evaluated separately at different doses using a completely randomized design with a 5 × 2 factorial arrangement (EO dose × substrate type). In a third 5 × 2 factorial design experiment, the potential of LEO to inhibit rumen methanogenesis was tested. The gas produced after 24-h of incubation (GP24) was stimulated and inhibited (P < 0.01) by LEO in CTS and RTS groups, respectively. The in vitro true dry matter (IVTDMD) and organic matter (IVTOMD) degradability were lowered significantly by LEO using CTS and RTS. A more pronounced fall was observed for total volatile fatty acids (total VFA) by LEO using RTS compared to CTS. The partitioning factor (PF) and NH3 were decreased and increased (P < 0.01) in CTS and RTS groups, respectively, but microbial biomass (MB) was linearly decreased by LEO in both CTS and RTS groups. An interaction effect between OEO dose and substrate type were observed for all parameters except the total VFA and MB which decreased linearly (P < 0.01) by OEO. The GP24, IVTDMD, IVTOMD and NH3 were decreased linearly (P < 0.01) by OEO using both substrate types. The PF was enhanced with OEO dose, but only in RTS group. Methane production was reduced linearly by LEO dose (P < 0.01), but the CH4/TG and CH4/CO2 showed linear and quadratic trends with LEO dose. An interaction effect between LEO dose and substrate type was also recorded for TG and CO2 (P < 0.01), as their production was stimulated and inhibited by LEO in CTS and RTS groups, respectively. Collectively, this study demonstrated that LEO and OEO affected ruminal fermentation differently depending on their doses and the type of substrate.