My old boy was 34 and I was away when he had to be put down. The stable owner called in the knacker man (with my consent) and I returned to an empty stable, having had him since he was 5.
Now to the worst part. I work on a pet stall on a market, and we buy our bones and pigs ears etc. from a pet warehouse which also has its own slaughterhouse. When we collect the stuff there are often skips with dead cows, goats, etc, in them, legs stuck up in the air, waiting to be 'processed' a pretty gruesome sight at the best of times. It wasn't till I got back from holiday that I found out the knacker man was the very same person we buy our bones off of, and for several months I could not bring myself to go to his yard to collect stuff, for fear of seeing my lad sticking out of a skip. I'm not normally emotional about things like this, I don't even have my dogs ashes back when they are cremated, but it did shake me up a bit to think I could be getting his bones back, and worst of all, paying for the privilege!
I consoled myself with the thought that he had a very good long life, and the end was without suffering. Some poor animals don't have that luxury.