To me, your statements seem weird.
For example, slaughtering them before the disease exhibits symptoms, means we are 100% preventing that pain. Thus, C is null, and void.
I don't get A. Properly treated cattle, such as in most of the world, are grass fed, or grass fed harvested hay, and free roaming. Thus, A makes zero sense, as A doesn't even take into account medical care (vaccination, antibiotics, vets, birth assistance), nor does it take into account immense protection from predation. Cows properly raised, live pampered, easy, happy, lives.
In terms of slaughter, old factory methods let cows horribly hang by their legs for hours, while they slowly bled out. Smaller concerns were more humane, but at least most of the world insists of quick, painless death for cattle. Where I live, it's destruction of the brain, such as a bullet, immediately stopping all thought, and frankly, far better than a death where (for example) wolves rip you apart while still alive, experiencing hours of agony.
(I have listened, where I live, at 2am to a pack of coyotes eating a large kill, its mewing, and cries of pain going on for more than an hour, it is NOT nice.)
I really think that if people care, really care, they need to stop basing opinions on false realities, and understand that often humans are far far far less brutal, than other animals.
Do you think a wolf takes care to kill a creature it is ripping apart? No. I just eats.
Cats "play" with mice, sometimes for hours before fully killing them. Mother cats also maim mice, so their children can learn.
Do you know why mice can breed from 2, to > 60, in a mere few months? To hundreds and hundreds in a year?
Because most of them are eaten alive, ripped apart while still living, by predation.
Nature is far, far more brutal than proper human animal husbandry.