My mother always said "Just because everyone does it, doesn't make it right". I've quoted her on SO many occasions, this being one of them!
For a long time I've considered the difference between the way we handle the deaths of our human families and friends, and the way we approach the deaths of our animals. Didn't make sense. I have thought that we just are not equipped, most of us, to handle the death of our animals, and get no guidance from our vets. Even my dear holistic vet suggested killing (I'm sorry, it would not have been euthanasia) my friend's dog a week ago. She said that she could not do anything more for her, and so she recommended killing her. My friend had the sense and instinct not to do that.
I was able to support him, and share my experience of natural death with him, and he is grateful, relieved, and happy. Gail Pope of BrightHaven has counseled him, bless her, and he has her guide, Soar My Butterfly, which lays out the dying process, what to expect, and what to do (mostly just be there, and be calm, with your animal)
Hospice for animals is a growing field, happily, and some of the sources of information are on my site, under Resources (www.beeholistic.com) Animals are adept in all things they do, and their dying is no exception!