An animal is also terribly inefficient at converting water and feed into human-consumable nutrients, because it's optimized for survival and reproduction.

The vat based solution is more scalable in the long run, and not impossible (we do it with beer).

> An animal is also terribly inefficient at converting water and feed into human-consumable nutrients,

I have an old book somewhere that says the milk cow is the most efficient means of converting a rocky hillside covered with grass into human-usable protein.

>a rocky hillside covered with grass

Yeah, that's scalable.

the cynic in me says that the "manages diseases" part will become increasingly untenable in the future, as antibiotic-resistant everything proliferate in feedlot environments, and american regulatory agencies fail to put a check on antibiotics mixed into animal feed.

reference: http://www.nytimes.com/2002/03/31/magazine/power-steer.html