30 day notice would be the max I would give and possibly less if there was something unforeseen that made expenses go up. Like flooding and it ruined the hay crop and hay doubled in price or something of that nature
As a boarder, I would expect 30 days notice. Just as when renting an apartment/house etc. However, in the event of an emergancy, I can see how 30 days could be basically impossible.
This is yet another reason I really liked the set up I was in when I was boarding. I had to supply my own bedding, and food, but board never went up, because it was just use of amenities!
If I had a boarder, and I supplied everything, I would do my best to give more than 30 days notice, as it is, in my opinion, unreasonable (except in extreme case, such as desaster as mentioned above) to expect somebody to stay and pay the new fee with no notice. Seem to me that would cause problems for the BO possibly more than it would for the boarder. I know I would seriously consider just leaving if I wasn't given notice of a board increase.
But, also as somebody else mentioned, board increase are usually smaller because they are spread over all boarders. Of course, if you are at a small barn, it could mean bad news for you