Let's start off with the simplest measure: calories per animal [show]:
If you think that the problem with eating animals is the fact that they suffer beforehand, then you are probably more interested with the suffering per year "title": "Age of animals slaughtered":
If, on the other hand, you think the problem is the fact that we are cutting animals' lives short, then you probably care more about the calories per day-of-life lost:
Of course, difficult questions still remain. Which of these animals deserve moral weight. Alternatively, how much moral weight do each of these animals deserve? Are these animals living in equally bad conditions?
These are not negligible questions. For instance, a naive approach of valuing animals proportional to the mass of their brains would cause a cow to be valued 111 times as much as a chicken per day "author": "Reflective Disequilibrium" - moving eggs directly below milk in our three tables. You may want to use neuron counts instead, but then the African Elephant beats out humans; if you switch to counting neurons in the cerebral cortex, then the long-finned pilot whale beats us out "title": "List of animals by number of neurons" - neither of these seem intuitive to me, but that may just be my human-bias speaking.