I haven't called off for sickness but I did take a vacation day when he was neutered. I think it's fine as long as you are doing it for a legitmate reason ie. sickness, surgery etc. Like someone else said, they are like your children and any responsible parent would take off work to make sure their dog or child is taken care of.
It also depends on who your boss is. My boss has a yorkie and a lot of other people on my team have dogs so they understand. As long as you don't abuse it.
