Do you know this by means of your mutant telepathic powers, or do you wander about the woods during hunting season looking for guys with rifles giggling? If the latter, please remember to wear bright colors as I would not wish for you to be shot accidentally.
I don’t think the dead cattle, swine, and sheep actually care how efficiently their carcasses are used. Were they capable of ratiociation and verbalization, I daresay they’d ask, in the most vehement possible way, to be spared the entire experience. It is their inability to engage in those two activities that makes killing them excusable.
Moreover, what does it matter how efficiently the carcass is used? Suppose a person is killed so that his organs may be harvested; his kidneys go to two different people, his liver is cut in half and used on two more, his heart goes to a fifth, and his blood goes to several others. We’ve saved a dozen human lives at the expense of one. Unless the dead person is Spider-Man, that’s probably a much more “efficient” use of his body than anything he could have done had he lived. But we still find that morally repugnant, because what makes the dead person a meaningful moral object in his personhood, not how cleverly we can use his body.