Research Article Received: 3 June 2013 Revised: 28 August 2013 Accepted article published: 14 September 2013 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jsfa.6396 In vitro screening of selected feed additives, plant essential oils and plant extracts for rumen methane mitigation Zoey Durmic, a,b* Peter J Moate, c Richard Eckard, c,d Dean K Revell, e Richard Williams c and Philip E Vercoe a,b Abstract BACKGROUND: Ruminants produce large quantities of methane in their rumen as a by-product of microbial digestion of feed. Antibiotics are added to ruminant feed to reduce wasteful production of methane; however, this practice has some downsides. A search for safer and natural feed additives with anti-methanogenic properties is under way. The objective of this research was to examine selected feed additives, plant essential oils and plant extracts for their anti-methanogenic potential in the rumen using an in vitro batch fermentation system. RESULTS: A significant reduction (P < 0.05) in methane production was observed with nine feed additives (up to 40% reduction), all eight essential oils (up to 75% reduction) and two plant extracts (14% reduction) when compared to their respective controls. Amongst these, only an algal meal high in docosahexaenoic acid, preparations of Nannochloropsis oculata, calcareous marine algae, yeast metabolites and two tannins did not inhibit microbial gas and volatile acid production. CONCLUSIONS: The current study identified some potent dietary ingredients or plant compounds that can assist in developing novel feed additives for methane mitigation from the rumen. c  2013 Society of Chemical Industry Keywords: plant extracts; essential oils; feed additives; rumen methane INTRODUCTION Ruminants produce large quantities of methane in their rumen as a by-product of the microbial digestion of consumed feed. Methane is a potent greenhouse gas and for this reason, much of recent research has focused on reducing ruminant methane production. 1 Feed additives are ingredients added to animal diets to improve food quality, promote growth, breakdown anti-nutritive factors, adsorb toxins, alleviate nutrient deficiencies and reduce energy- wasteful processes including production of methane in the rumen. While inclusion of antibiotic additives such as monensin to feed has been reported to reduce methane emissions in vitro, 2 results in vivo have not been consistent. 3 The use of antibiotics as feed additives is also associated with risk of developing antibiotic resistance in human pathogens, 4 and hence a search for safer components with anti-methanogenic properties is under way. 5 A variety of natural substances have been investigated as additives for livestock feeds, including yeasts, marine algae, plant derivatives and industry by-products, 6 but to date, only a few have been examined for their effect on rumen methane production. 7 Various marine products, in particular those rich in docosahexaenoic (DHA, C22:6ω-3) and eicosapentaenoic (EPA, C20:5 ω-3) acid have demonstrated significant anti-methanogenic potential. 8,9 While fish oil is abundant in these fatty acids, due to certain limitations for its use in ruminant feeds, various marine microalgae (i.e. Crypthecodinium cohnii, Schizochytrium sp., Nannochloropsis sp.) have been examined as potential source of these fatty acids. 10 Another interesting group of marine-based feed additives are calcareous marine algae products that are rich in calcium and magnesium and have been investigated as rumen buffers, 11 but their effects on methanogenesis have not been documented. Several yeasts have also demonstrated promising results in methane mitigation. 12 Further, industry by-products, such as various kernels and nut shells, 13 or their extracts 14 can have moderating effects on rumen methane production. Almond hulls have been examined as a potential feed for ruminants. 15 They also contain bioactive compounds such as linolenic and linoleic acid, tannins and/or triterpenoids 16 and antimicrobial ∗ Correspondence to: Zoey Durmic, School of Animal Biology, The University of Western Australia M085, 35 Stirling Hwy, Crawley, WA 6009, Australia. E-mail: zoey.durmic@uwa.edu.au a School of Animal Biology, The University of Western Australia M085, 35 Stirling Hwy, Crawley, WA 6009, Australia b Future Farm Industries CRC, The University of Western Australia M081, 35 Stirling Hwy, Crawley, WA 6009, Australia c DEPI Victoria, Hazeldean Rd, Ellinbank, Vic 3821, Australia d The University of Melbourne, 161 Barry Street, Parkville, Vic 3010, Australia e CSIRO Animal, Food and Health Sciences, Private Bag 5, Wembley, WA 6913, Australia J Sci Food Agric (2013) www.soci.org c  2013 Society of Chemical Industry