Antibacterial activities of a mixture of three plant extracts (Vangueria infausta, Peltophorum africanum and Eucalyptus globulus) were first evaluated using disc diffusion assay. Fermentation of two doses of the plant extract mixture (PE1and PE2; 0.3 and 0.6 g kg–1 of feed, respectively) were then compared in vitro with non-supplemented dairy cow’s basal diet and basal diet plus monensin (32 mg kg–1 of feed). Gas production was evaluated for 48 hours and crude protein degradability was determined using the Ankom DaisyII technique. A batch fermentation of diets was performed for rumen fermentation for 24 and 48 h. The plant extracts exhibited (halo zone > 9 mm) activities against all gram positive bacteria with no effects (halo zone < 9 mm) on gram negative bacteria tested. Gas volume was lower (p <0.05) for control than the rest of treatments. The effective degradability of crude protein was lower (p <0.05) with addition of MON, PE1 and PE2 compared to control. All additive (MON, PE1 and PE2) decreased (p <0.05) the rumen molar proportion of acetate. All additive (MON, PE1 and PE2) increased molar proportion of propionate. The plant extracts selectively inhibited gram positive bacteria and improved rumen fermentation similar to monensin.

Keywords: Aqueous extracts, Antimicrobial, Disc diffusion method, Rumen fermentation, Crude protein, Degradability.