very interesting, re: spirulina blocking the b12 receptor sites. I always wondered why it sounded good, but somehow didn't resonate, when it came to actally taking it.
About feces -- yes, rabbits apparently are one such animal that does well with reingesting; probably it is both the good bacteria and the b12.
I've heard the best source of probiotics (for us humans) is (an enema containing) the fresh feces of an infant. Considering "they" use the filtered proteins gathered from porto-potties (yes!!)to manufacture a 'drug' that benefits many, "they" no doubt have found a way to use the neonatal hospital feces.
However, best is that of a breastfed infant. You can look it up.