Note that there are developments in reducing the methane production of cattle. Supplementing their food with seaweed lets the bacteria in their gut fully digest the grass, breaking the methane to CO2
As it is if you removed the cattle and re-wilded the land they were on, that land would produce as much methane and CO2 as the cows did, as the same bacteria would break down fallen grass, or work in deer guts and no one will feed the wild land and deer seaweed