Just because it can't say 'moo' or move anymore, it's very nice for the human eye, but the animal is alive and the scientists don't actually know if it's suffering or not.
Things like the affectionate touch to your face, the knowing smile when you do something nice for someone, the tear in their eye when you are sad or have been hurt by life, the smile when you are happy and they are sharing in it, the arms that hold you close daily.