Think about America pre-colonization: a continent filled with ruminants happily munching away, being hunted at sustainable levels. To my mind that is peak sustainability and environmental friendliness.
That's with a population of on the order of 10 million for the entire continent: https://en.wikipedia.org/wiki/Population_history_of_indigeno...
Naturally grazing cows wouldn't even come close to sustaining the current demand for meat. Industrialized animal agriculture exists for a reason.