Manipulating rumen fermentation and methanogenesis using an essential oil and monensin in beef cattle fed a tropical grass hay

The objective of this study was to determine if a specific blend of essential oils (CRINA(R) Ruminants) compared to monensin could reduce enteric methane production in beef cattle fed medium to low quality Rhodes grass (Chloris gayana) hay. Five Brahman steers [mean live weight (LW); 226 kg] were allocated to one of five groups: control (no additive), CRINA1 (CRINA 1 g/d), CRINA2 (CRINA 2 g/d), Mon1 (monensin 60 mg/d) and Mon2 (monensin 250 mg/d) as a 5 x 5 Latin square. Individual LW, dry matter (DM, kg/d) intake, rumen pH, fermentation patterns, and ruminal fungal colonisation was measured. Methyl coenzyme-M reductase (mcrA) clone libraries (methanogen diversity) were generated from microbial DNA extracted from the rumen. Total methane production (g/d) was measured over 24 h using open circuit respiration chambers. The DM intake for animals given CRINA at either dose rate was not different (P>0.05) to the control (5.4 kg/d). However, Mon2 (P<0.05) reduced DM intake by 18%, compared with the control with no effect on rumen pH or total VFA production. CRINA significantly increased butyrate and iso-valerate concentrations compared with the control. Mon2 also reduced acetate:propionate compared with CRINA and the control. Based on sporangia counts from rumen fluid collected throughout the experimental period a reduction in fungal colonisation was observed for both monensin and CRINA treatments. The use of Monl or CRINA did not affect methane production. Mean methane production was reduced to 10.2 g/kg DM intake for Mon2 treated animals, compared with the control group (14.6 g/d DM intake), but this was also associated with lower DM intakes. A shift in methanogen diversity for monensin treated animals was due to a decrease in Methanomicrobium genus and concurrent increase in Methanobrevibacter genus. The specific blend of essential oils used in this study had no direct effect on methane emissions; however the potential to manipulate rumen fungi with CRINA and/or monensin and the relationship with methanogens may be a novel strategy to indirectly reduce enteric methanogenesis. (C) 2014 Elsevier B.V. All rights reserved.