in torture, the pain and discomfort is the point. prison is an excellent example of torture. by contrast, I think everyone agrees that we would prefer if no pain or discomfort were part of farming animals. this is probably especially true for the people actually doing the farming and slaughtering. in this case, the pain and discomfort are only incidental. it's not torture.
Everyone agrees? Really? So is humanity just collectively ignoring the alternatives? How is it possible that "everyone agrees" that you prefer no torture and pain, but the vast majority of people chose to engage in that practice? How can you live like that?
the question is why am I chaining them. I wouldn't do this because I think it is immoral to chain people up, but I don't need to invoke the spectre of torture to believe it's wrong.
If you're going to chain someone to the same spot for their entire life your intentions don't mean anything. Your act of doing it is what makes it torture.
torture is a specific thing. there may be a medical reason to do it. if I cut off your foot, that might be a form of torture, but if I do it because it's dangerous or mangled, it's a mercy. the intent matters. incidental pain is not torture.