The Microsoft co-founder has been outspoken about the environmental impact of meat production.
Methane is the most common greenhouse gas after carbon dioxide (CO2).
Livestock such as cows, goats and deer produce methane when their stomachs are breaking down hard fibres like grass for digestion.
This fermentation process creates methane gas which is then mostly belched out again.
University studies have shown that feeding cows seaweed could significantly cut their methane emissions.
Perth-based start-up Rumin8 is working on a dietary supplement – synthetically replicated from red seaweed – which stops the creation of the gas.
It announced in a statement that it had raised $12m (£9.7m) in a funding round led by Breakthrough Energy Ventures, which Mr Gates founded in 2015.
The investment firm is also backed by Amazon chief executive Jeff Bezos, and Chinese entrepreneur and Alibaba co-founder Jack Ma.
“We have been very pleased with the reception we have received from climate impact funds around the world,” Rumin8’s managing director David Messina said.
“There is a genuine desire to fund solutions to enteric methane emissions from livestock and fortunately for Rumin8, they can see the benefits of our technology,” he added.
Last October, New Zealand proposed taxing the greenhouse gases that farm animals produce from burping and urinating in a bid to tackle climate change.
The world-first scheme will see farmers paying for agricultural emissions in some form by 2025.
Almost half the country’s total greenhouse gas emissions come from agriculture, mainly methane.
In 2019, methane in the atmosphere reached record levels, around two-and-a-half times above what they were in the pre-industrial era.
What worries scientists is that methane has real muscle when it comes to heating the planet.
Individual methane molecules have a more powerful warming effect on the atmosphere than single CO2 molecules.
Over a 100-year period methane is 28 to 34 times as warming as CO2.