Effects of 3-nitrooxypropanol and monensin on methane production using a forage-based diet in Rusitec fermenters

• We investigated the effects of 3-nitrooxypropanol (NOP), monensin (MON) and its combination.
• Methane production was decreased by 71.5, 11.8 and 69.9% with NOP, MON and NOP plus MON respectively.
• The combination of NOP and MON was not additive.

3-Nitrooxypropanol (NOP) is an enzymatic inhibitor that has consistently decreased enteric methane (CH4) emissions in ruminants while monensin (MON) has a moderate, and sometimes transitory, effect on CH4 decrease. We hypothesised that combining NOP and MON would result in an additive CH4 decrease. The objective was to evaluate the effect of NOP (2 mg), MON (2 mg) and the combination of NOP (2 mg) and MON (2 mg) on CH4 production using a forage-based diet (600 g/kg barley silage, 350 g/kg barley grain and 50 g/kg vitamin-mineral supplement; dry matter basis) incubated in Rusitec fermenters. The experiment included an adaptation period without treatment supplementation (8 d), a treatment period (7 d), and a recovery period where treatments were discontinued (3 d). During the treatment period CH4 production (mL/d) was decreased (P < 0.01) by 71.5, 11.8 and 69.9% with NOP, MON and NOP + MON respectively. Hydrogen gas (H2) production was increased (P < 0.01) by 66.4 and 82.5% with NOP and NOP + MON respectively. The total copy number of the 16S rRNA gene for methanogens (log10 copies/mL) in the solid fraction, obtained using quantitative PCR, was decreased (P < 0.01) by 17.0 and 21.4% for NOP and NOP + MON, respectively. During the recovery period, CH4 production remained lower than control (P < 0.01) with NOP and NOP + MON treatments; however, a gradual increase in CH4 concentration was observed after treatment withdrawal. No effect (P = 0.53) on H2 production was observed during the recovery period. In conclusion, addition of NOP and, to a lesser extent, MON, to a forage-based diet is an effective means of decreasing CH4 production in vitro; however, the combination of both did not produce an additive effect.