A Nutritional Guide to Kefir for Dogs Kefir is a traditional fermented milk drink that has been used for centuries across many cultures. Today, it is widely appreciated for its naturally occurring live cultures and its role as a fermented food. When introduced thoughtfully, kefir can add dietary variety and natural fermentation compounds to a dog’s routine. This guide explores kefir’s origins, its nutritional characteristics, and how dog owners can choose and use kefir safely