Cows are a fairly major producer of methane, which is a potent greenhouse gas, contributing ~20-80x more to global warming than CO2 over the next 20-100 years.

Cows are a fairly major producer of methane, which is a potent greenhouse gas, contributing ~20-80x more to global warming than CO2 over the next 20-100 years. I do think it's interesting that there are different definitions / categories of "sustainable" right now - global warming sustainable, ecologically sustainable, resource sustainable - and they do seem to get conflated together.