A Comprehensive Review of Phytogenic Feed Additives and Rumen Manipulation Strategies for Mitigating Enteric Methane Emissions in Ruminant Livestock: Synergistic Effects, Microbial Mechanisms, and Sustainable Production

Enteric methane (CH₄) emissions from ruminant livestock represent a significant contributor to global greenhouse gas emissions and constitute a ۲–۱۲% loss of gross energy intake, thereby reducing animal productivity and environmental sustainability. The prohibition of antibiotic growth promoters in the European Union since ۲۰۰۶ has accelerated research into natural alternatives, particularly phytogenic feed additives (PFAs) derived from plant secondary metabolites. This comprehensive review synthesizes findings from recent in vitro and in vivo studies investigating the efficacy of essential oils, tannins, saponins, flavonoids, and other plant-derived bioactive compounds in modulating rumen fermentation, reducing methanogenesis, and improving animal performance. The synergistic interactions between specific essential oil combinations, particularly cinnamon leaf oil with peppermint oil (۸۰:۲۰) and anise oil with clove leaf oil (۸۰:۲۰), demonstrate superior efficacy in reducing CH₄ production while maintaining volatile fatty acid profiles. Condensed tannins and hydrolysable tannins exhibit dose-dependent anti-methanogenic properties through direct inhibition of methanogenic archaea, reduction of protozoal populations, and decreased hydrogen availability. Fenugreek (Trigonella foenum-graecum L.) supplementation has shown CH₄ reduction ranging from ۱۵–۷۲% in various in vitro studies, attributed to its rich saponin, tannin, and flavonoid content. Calliandra calothyrsus supplementation at ۴۰% of dietary dry matter reduced CH₄ yield by ۳۰% and improved animal health through anti-parasitic effects. Meta-analytical evidence indicates that nitrate, saponins, oils, biochar, and ۳-nitrooxypropanol (۳-NOP) are effective CH₄ mitigating strategies, with oils and ۳-NOP providing co-benefits for milk production and composition. Genetic selection for low CH₄-emitting animals, incorporating heritability estimates of ۰.۱۲–۰.۴۵ for CH₄ traits, offers permanent and cumulative emission reductions. This review identifies optimal PFA combinations, elucidates mechanisms of action, and proposes integrated strategies combining nutritional, genetic, and microbiome-driven approaches for sustainable ruminant production

کلیدواژه ها:

methane emission ، essential oils ، phytogenic ، rumen fermentation ، methanogenesis