3-NOP: Effective methane inhibitor in dairy cows

The researchers noted that some previous studies have shown consistent effects of 3-NOP on enteric CH₄ emission. However, these studies have not conclusively determined its effects on milk production and composition, which is important for future adoption of this CH₄ mitigation practice. Therefore, they focused their research on both the reduction on enteric methane production and the effects on milk production and composition.

Compared to the control group, 3-NOP applied at 60 mg/kg feed dry matter decreased daily methane emission, emission yield, and emission intensity. Photo: Zana van Dijk

Due to its molecular structure, 3-NOP is highly soluble and rapidly metabolised in the rumen where it has its beneficial effect. The 3-NOP molecule is a specific inhibitor of methyl-coenzyme M reductase, the enzyme involved in the biological synthesis and anaerobic oxidation of CH₄ in methanogenic archaea. To be specific, 3-NOP inhibits the reduction of CO₂ by dissolved H₂ to form CH₄ by targeting the active site of methyl-coenzyme M reductase in the terminal step of methanogenesis in the rumen.

The study: Effect on methane emission & milk production and composition

The study examined the effect of 3-nitrooxypropanol (3-NOP) on enteric methane emission, and milk production and composition in Holstein dairy cows. A total of 48 multi- and primiparous cows averaging 43 kg/d milk yield and weighing about 594 kg were randomly assigned to 2 treatment groups:

1. control, no 3-NOP
2. 3-NOP supplemented at 60 mg/kg DM feed.

The authors also evaluated a dose-response effect of 3-NOP when supplemented at 40, 60, 80, 100, 150, and 200 mg/kg of DM feed.

Reducing enteric methane production

Compared with the control group, 3-NOP applied at 60 mg/kg feed dry matter decreased daily methane emission, emission yield, and emission intensity by 26, 27, and 29%, respectively. The CH₄ per energy-corrected milk was also decreased by 29%. When a dose-response test was employed, the 150 mg/kg feed had the highest methane reduction percentage (36%), although the difference between 100, 150, and 200 mg was not significant. To further assess the anti-methanogenic effect of 3-NOP, the researchers measured the production of hydrogen; this was 6-fold greater for 3-NOP cows over the 15-week treatment period compared to the control group. They mentioned the increase in H₂ emission to be directly associated with the inhibition of methanogenesis by 3-NOP, since methanogenesis is one of the main H₂ sinks in rumen fermentation.

Figure 1. Effect of dietary supplementation with 3-NOP on enteric methane reduction in dairy cows

Milk production and composition

The dry matter intake, and milk yield and lactose content were not affected by 3-NOP supplementation at 60 mg/kg DM feed. On the other hand, the energy-corrected milk yield, milk true protein, and milk solids were increased. Interestingly, milk fat concentration and yield were also increased by 3-NOP; this was attributed to increased concentration of de novo synthetised short-chain fatty acids in milk. In addition, supplementing 3-NOP at 60 mg/kg reduced the somatic cell counts by 37%.

Energy availability and feed utilisation efficiency

According to previous studies, enteric CH₄ represents an energy loss of 2-12% of the total feed energy consumed by ruminants. Although it has been suggested that inhibition of methanogenesis may provide extra ME that can be used for production purposes, in this study, 3-NOP inclusion did not increase milk yield, neither did it improve feed utilisation efficiency. The researchers pointed out that the extra ME energy from inhibited methanogenesis was possibly redirected towards milk fat synthesis – concentrations of de novo synthesised fatty acids in milk fat were increased by 3-NOP, suggesting increased energy availability.

These results suggest that 3-NOP is a promising feed additive for reducing enteric CH₄ emissions, maintaining lactational performance and potentially increasing milk fat yield,”

Administration and dosage

They concluded that the administration of 3-NOP via the total mixed ration at an inclusion range of 0 to 200 mg/kg DM feed decreases enteric CH₄ emissions by 22 to 40%, and the emission intensity by an average of 33%. Maximum mitigation effect of 3-NOP was achieved at 150 mg/kg DM feed, but no significant differences were observed among the 3 highest doses (100, 150, and 200 mg/kg). DM intake and milk yield were not affected, but milk fat concentration and yield were increased, suggesting increased energy availability. In a similar study, researchers determined the effect of 3-NOP on enteric methane emissions when 3-NOP was mixed in with roughage or incorporated into a concentrate pellet: their results showed that 3-NOP can reduce enteric CH₄ emissions when incorporated into a concentrate pellet and that this reduction is not different when 3-NOP is mixed with the basal diet (roughage). This broadens the possibilities of using 3-NOP in the dairy sector worldwide, since provision of additives mixed in the basal diet is not always feasible.

“These results suggest that 3-NOP is a promising feed additive for reducing enteric CH₄ emissions, maintaining lactational performance and potentially increasing milk fat yield,” they concluded.

This article is based on the original article by A. Melgar, C. F. A. Lage, K. Nedelkov, et al. 2020. Enteric methane emission, milk production, and composition of dairy cows fed 3-nitrooxypropanol. J. Dairy Sci. 104:357–366. 10.3168/jds.2020-18908.