I went on a tour through a slaughterhouse when I was a teen, as part of a school trip. Didn't want to go, but my stepfather decided that it would be "good for" me. I made it clear I didn't want to go and he laughed. He loved the power trip of forcing me to watch animals be killed.
It really messed me up. I won't eat red meat mostly as a result of this, but also because my family were also ridiculously poor cooks. (They were so bad that you wouldn't believe it.)
The smell of the animal fat has stuck with me for nearly thirty years, I can even smell it overpowering the fragrance of perfumed soap. Hand sanitizer, pump soap, and vegetable based soap are fine, but if I have to use ordinary animal soaps, the smell reminds me of what I saw.
I watched a cow be electrocuted, "stunned" they called it. The guide told me that it didn't feel anything because it was in a deep state of shock.
Ever been shocked by a cattle electric fence? When I was 9, I was. You can't move immediately afterward because of the shock of the event, and when the second blast hits you it hits really hard. I felt three of those, it was only when the third struck that I could move, and have no doubt that they were agonizing.
Shocking an animal to stun it, so you can slit its throat and let it die painfully while you dismember it, is no happy little picnic for the beast. This is no easy, painless death. I'm sure it would be agonizing and drawn out over several minutes, and by the time the animal recovers from the shock enough to express its suffering, it's already in pieces and can't.
Roll on lab-grown meat.
Side note: not completely relevant, but I have been attacked by a dog, and I was in shock through that as well. The worst injuries really hurt, but the adrenaline from the attack made me able to get away from the dog. The minor skin injuries I couldn't feel, because the pain centers were being overwhelmed by the worse ones. Between this, and the cattle electric fence, I'm sure they suffer.