I am quite fond of water kefir and kombucha tea, both of which I make myself. There is plenty of info on how to do this on the internet. When I have extra "grains" which are rich in probiotics I'll give a tbsp. or so in each horse's feed. The "grains" multiply so one can keep it on going. The KT is full of probiotics also. It uses a SCOBY which is often referred to as a mushroom, which it's not, and looks like a piece of wet rawhide when floating in the jar. KT takes longer to brew, at least several weeks.