Effect of herbs and spices (plant extracts) on rumen microbial activities: a review

Abstract

Ruminant livestock are important sources of animal protein and calories, also are sources of global greenhouse emissions. There is increasing interest in evaluating the potential of natural antimicrobials such as plant extracts to modify rumen microbial fermentation due to reduction on the use of antibiotics in animal feeds and with ban on antibiotics in the Europe. These compounds are known to have an impact on rumen microbial metabolism by inducing changes in the fermentation conditions and also affecting ruminant productivity. The methods to effectively reduce methane production in the reticulo-rumen include processing of feeds, altering the diet, supplementation of unsaturated fatty acids, defaunation, supplementation of organic acids, halogenated compounds, ionophores, microbial feed additives (probiotics), plant extracts and their secondary metabolites. All these strategies to be validated in vivo studies in specific dose(s) to make it economically viable. This review aimed to reveal the impact of these natural plants extracts on rumen microorganisms. Plants normally contain a high to medium content of secondary compounds such as essential oil, saponins, organosulphur and tannins, which exert a specific effect against or favour rumen microorganism and reduce methane, leaving less or no distortion on the remaining rumen biomass. Their actions include direct action on microbial metabolism and deprivation of substrates for microbial growth. These plant extracts require more long term studies in vivo to determine their effectiveness in commercial systems. For sustainability, the feed additive would need to be effective over long periods of time, non-toxic for animals, the environment, the consumers and maybe standard use in animal feeds