In vivo methane abatement by pyromellitic diimide in sheep and redirection of rumen hydrogen by co-administered feed additives.

Pyromellitic diimide (PD) has been shown to reduce enteric CH4 emissions in vitro, but no research has yet quantified CH4 reduction potential of PD in vivo. It is proposed that a combination of CH4 inhibitors, such as PD, rhubarb extract (RE), or monensin (MO), and hydrogen acceptors, such as fumaric acid (FA), could improve the mitigation of CH4 and direct hydrogen to other sinks. This study is the first to assess the combined effects of PD, RE, MO, and FA on intake, ruminal fermentation, and CH4 emissions in sheep. Forty-eight Merino-cross sheep were housed in individual pens and allocated to eight dietary treatments in a complete block design, for a 35-d feeding period. Experimental diets were based on alfalfa pellet mixed with 1.0% canola-oil, alone (Control) or with addition of 50 mg/kg DM of PD, 250 mg/kg DM of RE, 30 mg/kg DM of MO, or 2,000 mg/kg DM of FA, and the combined mixtures of PD + RE, PD + RE + FA or PD + RE + FA + MO. Enteric CH4 emissions were measured weekly for 5 wk. The additives did not alter DMI, average daily gain, feed efficiency, or body condition score. Supplementation of PD reduced (P < 0.01) CH4 production, yield, and intensity by 74% to 79% compared with Control (P < 0.01), but no further improvement in CH4 reduction was observed when PD was combined with other additives. Dissolved CH4 in rumen fluid was reduced and dissolved H2 was increased 8-fold by PD alone (P < 0.01). When RE was added alongside PD (either alone or in combination with FA or MO), dissolved H2 remained elevated above Control levels, but was approximately half that observed with PD alone, suggesting that RE, FA, and MO facilitated the redirection of hydrogen toward alternative fermentation pathways. The combination of PD + RE increased (P < 0.01) butyrate concentration by 1.34-fold, compared with Control, while the combined supplementation of all additives (PD + RE + FA + MO) increased (P < 0.01) the molar proportion of propionate (by 1.34-fold) and deceased the proportions of acetate (by 0.92-fold) and the acetate-to-propionate ratio (by 0.39-fold) compared with Control. In conclusion, supplementation of PD alone or combined with RE, RE + FA, or RE + MO + FA can reduce CH4 emissions, and when combined with rhubarb extract, can redirect hydrogen to other sinks in sheep without compromising intake or performance.