So in that case, you'd be okay with humans being bred with the sole purpose of being organ donors when required? After all, they wouldn't have existed if they weren't meant for that.

And before you say that it's different because humans are sentient, so are pigs and cows. Pigs are some of the smartest animals on Earth and cows can feel most emotions humans can, recognize individual humans and each other, and feel grief when they have their calves taken away.

Their lives are exactly as drawn out and happy as possible, because we created those animals and the amount of happiness they could have ever experienced.

Except that's bullshit; their happiness and well-being is never taken into consideration. They're constantly crowded. Some of them hardly ever move(dairy cows, egg laying hens, and pig sows used for breeding almost never leave their enclosure, and some of them physically can't leave). They spend almost their entire lives panicking and, in the best case, misery, and worst case, constant physical pain.