Putting the supplement into the diets of 40 wagyu cattle in an Australian feedlot [emphasis added]

again, testing on grain fed cattle with no mention of the comparison with grass-fed/pastured cattle

from what I’ve stumbled across

• grass fed cattle do produce more methane (byproduct of longer digestion times) – but seaweed or daffodil supplements could just as easily be added to their diets
• feed corn and grain introduces a whole slew of gastrointestinal problems and health issues that have to be dealt with with regular supplements and antibiotics
• holistic management (intensive rotational grazing) produces great results with water retention and carbon sequestration that could easily offset the methane production

But it made them fart 28% less. Still good to know.

These are beef cattle according to the article, not dairy cows. We know the answer on meat.