The idea that animals DO indeed ingest their own feces is supported by Gabriel Cousins...
He states that although bacteria in the human intestinal tract manufactures vitamin B-12 it cannot be absorbed into the body. He goes on to say that gorillas on occasion will ingest their own feces and states that other vegan type animals do the same. His theory is that they consume their own feces in order to acquire the B-12 from the feces. Studies were even performed using human subjects to have them take their own feces to balance out B-12 deficiencies...and it worked.
Cousins is not a proponent of using algaes as a source for B-12 because its in an analog form of the vitamin that blocks the receptor sites for B-12 thus actually lowering B-12 levels in the body.
So Spirulina is out as a source for B-12 is it has negative repurcussions.