[SimonandSyril]

The dwarf species are immune to wet tail so it is most likely a dietary problem. Its hard to tell with campbells and winter whites to tell if they're hybrid or not. Just in case try to limit the sugar intake as hybrids do develop diabetes. If I were you I would get the old food mix and use it for a while, slowly mix in some of the new food mix more and more each time you fill the bowl. Do the same with vegetables. Start off with a small amount and slowly increase. Sudden changes to food and diet can cause bowel problems.