yeah..you're not supposed to just change an animal's food all of a sudden like that. it'd be like you only eating bread your entire life, and then one day we take away bread and just give you broccoli. you'd puke your guts up, because what the hell is this green stuff and where's my bread?! try mixing 75% old food with 25% new food for a few days, then 50%/50% , then 75% new and 25% , then 100% the new stuff.

That's how anti hairball food works. It's hard to cough up a hairball while puking