I'm not sure what it is, Mordy, but buttermilk has helped several of my critters when they had digestive dilemmas. Especially CJ, a cat my Mom had. CJ was short for "Crapper John." The cat had a terrible problem controlling his bowels until we found out he liked buttermilk. A little bit of buttermilk everyday, or yoghurt sometimes for a change, and he never had the problem again.
Maybe you can tell me why that worked so well, all I had to really go on were old wives' tales, which, I've found, are often very good advice!