Again, the problem is Methane.
Cows eat carbon (and other stuff) that's stored in grass. Their digestion then converts that into Methane and farts it out. This Methane is much worse than the carbon that was part of the cycle.
This was not a problem in the past, because the world population of cows was probably a few million. Today, that population is almost a billion.
Most things in climate science are a question of scale. If the total human population were 9 million, i.e. the equivalent of Portugal or New Jersey, they could be burning coal and driving SUVs with no major impact on the climate.