I can't re-find the post, but I'm pretty sure that a while ago Bryan Caplan made the following argument:
1. Most animals that will get eaten only live because they will get eaten.
2. The utility of living is positive, and hence bigger than the utility of never having been born, which is zero.
3. Hence, if you care about animals, you should eat as much meat as you can.
I think that's an original and fascinating argument. I also think it's a bit simplistic.
I see two problems with Bryan's argument. As for pt. # 1, most fish are not alive because they're meant to be eaten. What's more, if you kill a fish, you obviously reduce its chances of reproducing to zero, preventing their potential offspring's lives.
As for pt. # 2, the problem, of course, is that if you ask animals about the utility they get out of life, they're not going to answer. So you have to do some wild guessing. My guess is that chickens that are held in cages, the typical base of which is 25 square centimetres, get negative utility out of life, while the average cow and pig is getting positive utility out of life.
If the above reasoning is correct, it follows that you shouldn't eat fish and chickens, but you should eat pigs and cows. If you care about animals, that is.
A related post