My dog has really stinky and loud gas!?

I have been giving my dog the "Herring Meal" Natural Choice kibble since I've had her, about a year. There has been a shortage of herring for the past few months, so I switched over to another formula of the same company, a chicken based food. My dog has had really loud and horribly stinky gas since I've switched over, a few weeks ago, along with loose stools for the past few days. She never used to! I dont' know what to do, as this formula is supposedly for sensitive stomachs, like the other one I was using.