I use Protexin, but it doesnt seem to be the same Protexin as in Australia (which is now Pron8ure). The one’s I have contain a strain of saccaromyces cerevisiae (brewer’s yeast) which occurs naturally in the healthy rabbit gut.
I also have capsules with enterococcus faecium, which I can see that Pron8ture probiotics also contain. It is a bacterium that also is highly prevalent in the healthy rabbit gut. Lactobacilli are not beleived to be of much use for rabbits, but many rabbit owners still find them helpful, and tbh, noone really knows how the various microorganisms interact in the gut, because its an incredibly intricate interplay. It is an area of intensive reasearch though. We humans depend a lot on our gut microbes, but rabbits do so to an even greater extent, because they rely more on gut microbes than on digestive enzymes.
What seems clear is that probiotics wont hurt -if the rabbit gut cant use it, or if the microbes perish in the highly acidic environment in the rabbit stomach, it just gets pooped out – as will any surplus (so you cant really overdose unintentionally).