Methane emissions from agriculture account for 11% of total national greenhouse gas emissions, with the majority coming from dairy, beef and sheep production systems. Practical abatement strategies targeting enteric methane are essential if these industries are to curb emissions and benefit from the Carbon Farming Initiative.
The project’s emphasis was on evaluating abatement strategies that are practical and which can be readily adopted by livestock farmers in south eastern Australia.
Researchers evaluated the effect of various dietary supplements on enteric methane production in ruminants through a structured process of in vitro screening of various forage and dietary supplement options, followed by in vivo evaluation of the methane abatement and production impacts of feeding forages and supplements.
Screening focused on alternative forages being studied in other feed-base projects (30:30, EverGraze) plus development work on culturing micro-algae on effluent ponds as a source of dietary oil and commercially available tannins and enzymes from the paper industry.
Promising forages and supplements were tested in vivo using the SF6 method in the field, with the Open Circuit Respiration Chambers then being the last step in definitively quantifying the methane abatement potential of the most promising sub-set of these options.
The project also validated Open Path Fourier Transform Infra-red Spectrometer methane measurement technology as a useful standard method of measuring methane emissions from grazing ruminants.
The study showed that the addition of a fatty feed supplement to a diet — including oils in brewers grains, cold-pressed canola and hominy meal — reduced methane emissions from dairy cattle by 3.5% for every 1% increase in the total fat concentration in the diet. These findings are expected to form the basis of a dairy industry Carbon Farming Initiative methodology.
The tannin and oil-based supplements dried grape marc and ensiled grape marc reduced methane emissions from cows by approximately 20% without decreasing feed intake or milk yield, or having adverse impacts on milk composition.
Although the research indicates that dietary supplements of fat and tannin inhibit methane emissions from ruminants, scientists showed that simultaneous feeding of fat and tannin supplements may not have an additive effect, when added as extracted components. This novel finding has important implications for dietary methane mitigation strategies that are based on multiple dietary supplements.
Feeding cows on practical levels of algae meal containing high concentrations of DHA did not reduce methane emissions but resulted in milk with lowered milk-fat concentration. This finding is important because it is contrary to international in vitro studies that had reported algae meal high in DHA had potent anti-methanogenic properties with the potential to decrease methane emissions by 75%.
The grazing experiments evaluated an open path tracer technique for measuring methane emissions from sheep, establishing it as a reliable method with great potential for use in future on-farm demonstrations of methane mitigation feeding and management strategies.
This research has now led to the development of the first Carbon Farming Initiative offset methodology for enteric methane reduction, currently under review by the Domestic Offsets Integrity Committee.
This project was part of the national Reducing Emissions from Livestock Research Program, funded by the Australian Government Department of Agriculture, Fisheries and Forestry under its Australia’s Farming Future Climate Change Research Program.