What question did this study set out to answer?

The central aim is to evaluate how different plant essential oils affect ruminal fermentation characteristics in vitro.

February 20, 2026Open Access

Effects of Plant Essential Oils and Their Combinations on In Vitro Ruminal Fermentation Characteristics

Key Points

The central aim is to evaluate how different plant essential oils affect ruminal fermentation characteristics in vitro.
Evaluated eight plant essential oils (verbena, cinnamon, rosemary, Torreya grandis, ginger, fennel, thyme, oregano)
Conducted 24-hour in vitro fermentations at varying doses (0, 0.75, 1.5, 3, 6%)
Assessed dry matter degradation, microbial protein synthesis, volatile fatty acid production, and nitrogen metabolism
Created five essential oil blends for further analysis
3% cinnamon oil significantly improved dry matter degradation and microbial protein synthesis efficiency
1.5% fennel oil increased microbial protein and total volatile fatty acid concentrations
0.75% thyme oil enhanced nitrogen utilization without affecting ammonia levels
T2 blend significantly outperformed others in nitrogen metabolism and dry matter degradation, while reducing methane production
Increased microbial diversity observed alongside elevated abundance of Selenomonas and Succinibacter

Abstract

This study aimed to evaluate the effects of eight plant essential oils on in vitro ruminal fermentation. The oils tested were verbena (VE), cinnamon (CE), rosemary (RE), Torreya grandis (TG), ginger (GE), fennel (SF), thyme (TE), and oregano (OE). Each was supplemented at five graded doses (0, 0.75, 1.5, 3, and 6% of the substrate DM) during 24 h incubations. The results demonstrated that adding 3% CE significantly increased the in vitro dry matter degradation rate (IVDMD) while enhancing microbial protein (MCP) synthesis efficiency and acetate concentration. The addition of 1.5% SF increased MCP and total volatile fatty acid (TVFA) concentrations without affecting ruminal ammonia nitrogen levels, and 0.75% TE enhanced nitrogen utilization efficiency while maintaining primary fermentation pathways and ammonia nitrogen levels. Although 0.75% OE did not alter overall fermentation intensity or nitrogen metabolism, it specifically regulated volatile fatty acid metabolic pathways, significantly promoting butyrate production. Through preliminary screening, four essential oils (CE, SF, TE, OE) that positively influenced rumen fermentation were selected and combined into five distinct blends: T1 (CE + SF + TE), T2 (CE + SF + OE), T3 (CE + TE + OE), T4 (SF + TE + OE), and T5 (CE + SF + TE + OE). In vitro 24 h fermentations with varying inclusion levels (0, 0.75, 1.5, 3% of the substrate DM), in comparison with the CON, showed that the T2 group significantly outperformed the other four formulations in nitrogen metabolism and IVDMD, while substantially reducing methane content. Simpson’s index of microbial diversity was markedly elevated, alongside an increased relative abundance of key bacterial genera—Selenomonas and Succinibacter. Considering comprehensive performance metrics and economic viability, the 1.5% T2 was selected as the optimal formulation.

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