[hannob]

The main energy input for meat from animals is the sunlight shining on the plants that the animals eat.

The efficiency of that is utterly terrible. That's also the reason why any form of bioenergy from crops has such huge landuse requirements. It is likely almost impossible to do any worse with any technological process.

[bayesian_horse]

That's not really true. The energy used in the cultivation of their feed usually has the highest carbon footprint of the whole equation. "Grass-fed" and similar approaches don't scale up to the demand of meat. They require more land and more labor, all of which increases prices and increases competition for labor and arable land.