User blog comment:Unownshipper/Flora and Fauna of Rapture/@comment-6024608-20131019124102/@comment-6024608-20131020030731

Goats and chicken eat less for thge amount of meat they produce (and cheese you need some milk to make).

To produce all the grains (staple of most civilizations) you have a byproduct of the rest of the plant (even if less by using dwarf varieties), which the other animals would be fed (including cows, but they would be somewhat more expensive)..

Even with cheaper protein substitures (soybeans) you still have that leftover vegetation which could be used (and IS used in RL)  as animal feed. I recal 'silage' is partially fermented (adding yeast to add additional nutrients)....