Biochemical Properties, Antioxidant Activity and <em>In Vitro</em> Ruminal Fermentation of Four Medicinal Plants (<em>Polypodium vulgare, Chamaemelum nobile, Ocimum Forsskaolii</em> Benth, and <em>Lavandula stoechas</em>) Cultivated in Northwestern Tunisia

Background: The ethnobotanical use of medicinal plants is a widespread practice worldwide, serving various therapeutic and practical purposes due to their phytocompounds. This study investigates the chemical composition, antioxidant capacity, and in vitro ruminal fermentation properties of four plant species: Polypodium vulgare, Chamaemelum nobile, Ocimum forsskaolii Benth, and Lavandula stoechas. Methods: The chemical composition, including insoluble dietary fiber and phenolic compounds, was determined. Antioxidant activity was assessed using DPPH, and HPLC identified key bioactive compounds. In vitro fermentation trials evaluated gas production, metabolizable energy (ME), organic matter digestibility (OMd), and volatile fatty acid (VFA) production in sheep and goats. Results: All species contained high levels of insoluble dietary fiber, with L. stoechas exhibiting the highest neutral detergent fiber (62.39%) and hemicellulose (56.74%). C. nobile had the highest polyphenol and flavonoid levels (73.88 &plusmn; 0.79 mg GAE/g DW and 27.85 &plusmn; 0.54 mg QE/g DW, respectively), along with strong antioxidant activity (IC₅₀ = 0.38 mg/mL). HPLC identified catechol in P. vulgare, ferulic acid in C. nobile, chlorogenic acid in O. forsskaolii, and apigenin in L. stoechas as major compounds. In vitro fermentation showed that C. nobile and O. forsskaolii at D20 produced the highest gas volume. ME, OMd, and VFA production increased, with a greater effect in sheep than in goats. Conclusion: These findings highlight the potential of these plant extracts, rich in bioactive compounds, to offer a sustainable alternative to conventional feed additives by enhancing ruminal fermentation, energy efficiency, and livestock performance.