You have every right to expect quality care as a paying boarder, just remember that you are dealing with humans : ) I don’t know the circumstances at your barn like what time they feed, how many times this has happened to you, how many different people are in-volved with the barn chores, things like that. I am the consummate string-nazi as they are plastic now, for the most part, and the plastic twine does NOT break: not good for cross-ties any more : ( .. I also worry more about them getting tangled in it than eating it. I now insist that the twine be cut from a bale, not pulled off like I used to do.
Thing is, as careful and demanding as I am, once in a while a string sticks to a bale or flake and ends up going out with the hay, not often, but it happens. I admit sometimes I am feeding in the dark and don’t catch a string, not often but it happens. If it is happening regularly at your barn, you have more of an issue. Mention it to the manager, definitely, but be forgiving of the first time, ‘specially if you have been there for a while and this is an isolated incident. Horses live in the barn. The barn is run by humans and no-one that I know of has achieved perfection yet : )
Sure there's right and wrong but mostly there's just a whole lotta different.