No, but they are capable of feeling pain. You're almost there with equating how we treat dogs and how we treat cows. Maybe it should go in the other...
It could be that he knows what he wants to say but can't get the words out, it isn't necessarily dementia. Like I say, they might as well be the same...
Is there evidence that he has dementia beyond his disordered speech? Do we know/suspect that his reasoning is affected? Obviously being able to speak...