In America, it mostly comes from farm subsidies. Subsidies on feed corn and feed soybeans make it cheaper to buy feed than to grow it yourself. So, rather than

In America, it mostly comes from farm subsidies. Subsidies on feed corn and feed soybeans make it cheaper to buy feed than to grow it yourself. So, rather than grow feed on the same farm, fertilized with manure, farmers buy feed trucked in from neighboring states fertilized with chemicals, much of which is petroleum based, and discard the manure. And, then there are the cow farts full of methane. Methane is apparently a much more potent greenhouse gas than carbon. I’ve heard for over a decade that there is some seaweed-based supplement that dramatically cuts methane from cows. But, I guess farmers have had no motivation to buy it yet.