A novel methane inhibitor feed supplement, 3-nitrooxypropanol (3NOP), reduces methane emissions. The efficacy of 3NOP varies widely though, showing no methane emission reduction in some trials up to 85 percent reduction in others.
Research conducted by a team of scientists from the Netherlands, United States, and Canada identified the level of fibre in the diet, the type of cattle (dairy vs beef), and the dose of 3NOP to explain a large part of this variation in response to 3NOP. Such insights are important because methane emissions from ruminants represent a significant portion of global greenhouse gases blamed for causing climate change.
The scientists carried out a meta-analysis of 11 studies in dairy and beef cattle. In these studies, 3NOP added to the feed reduced methane emissions by on average 30 percent.
Dietary fibre affects efficacy of supplement
A major finding of the research was that the efficacy of 3NOP in mitigating methane emissions is smaller when the fibre content of the diet is greater. For every 50 g increase in fibre per kg feed, the reduction in methane emission by 3NOP was 8 percent smaller. Thus, greater levels of NOP are required for high fibre diets to decrease methane emissions.
Humans cannot effectively use fibre rich plant material, such as grass, as food. By virtue of microbial fermentation in the rumen, ruminants are capable at using plant fibre for production of meat and milk that humans can consume.
“Ruminants provide a key role by converting fibre-rich feed ingredients, not competing with direct human food production, into important sources of nutrients for human consumption”, said lead researcher Jan Dijkstra of Wageningen University & Research (the Netherlands). “Increases in dietary fibre level are generally associated with greater methane emissions. Our finding that the efficacy of 3NOP to reduce methane emissions is dependent on the level of fibre in the diet, is therefore of great significance in view of the shift towards high-fibre diets for cattle, whilst reducing the carbon footprint of cattle production”.
Efficacy less in beef cattle than in dairy cattle
A surprising result was the difference in response to 3NOP between dairy and beef cattle. When adjusted to the same 3NOP dose and diet composition, the methane mitigating effect of 3NOP was less in beef cattle (22 percent reduction) than in dairy cattle (39 percent reduction).
“Both for practical application as well as for inventory reports, the finding that 3NOP works more effectively in dairy than in beef cattle is of large significance”, Dijkstra said. “This greater efficacy is likely associated with higher feed intake level in dairy cattle. The higher intake increases hydrogen concentrations in the rumen of cattle, which favours routes of hydrogen disposal other than through formation of methane. In such conditions, smaller amounts of 3NOP are required to decrease methane emissions”.
Dose of 3NOP enhances methane mitigating effect
The research team found also clear evidence that the amount of 3NOP added to the diet enhances the 3NOP methane mitigating effect. 3NOP specifically inactivates the enzyme methyl coenzyme M reductase, which is the key enzyme responsible for producing methane by micro-organisms in the forestomachs of ruminants. Adding more 3NOP to the diet inactivates a greater amount of this enzyme, leading to more pronounced reductions in methane emissions.
The study was published this month in the Journal of Dairy Science (article in press; https://doi.org/10.3168/jds.2018-14456). Researchers from Wageningen University & Research (the Netherlands) (J. Dijkstra, A. Bannink, S. van Gastelen), the University of California, Davis (USA) (E. Kebreab) and the University of Guelph (Canada) (J. France) were involved in the study. For further information, please contact Dr Jan Dijkstra (e: firstname.lastname@example.org).