It's probably not the buttercup. With all the other good snacks, they may be avoiding it. I try to keep the undesirables from spreading (so, usually cut at budding or flowering).
It's more likely, if they are new to you, they have loose stools because their immune systems take a hit from relocation. Try immune boosters and keep charcoal on hand in case they get into anything toxic. You can run a fecal to see if there is a parasite you should be treating, and check FAMACHA.
It's more likely, if they are new to you, they have loose stools because their immune systems take a hit from relocation. Try immune boosters and keep charcoal on hand in case they get into anything toxic. You can run a fecal to see if there is a parasite you should be treating, and check FAMACHA.