It isn't the "cow farts" that produce most methane, but rather the anaerobic processing of cow dung emanating from feed lots, dairy operations, etc.

Grass-fed beef cattle whose dung is "recycled" in a more natural way in the fields produce the same emissions as would wild ruminants such as antelope, bison, etc.

The biodiversity problem in the above refers mostly to new land clearances intended for farming, including for feedstock. This is minor in N. America and Europe, mostly as the clearances were done decades or over a century ago.