[paul.fr]

I have seen birds eat vomit, and dogs eat poo! Why do they do this?

[DoctorBeaver]

I can't tell you about birds, but coprophagia is quite common among dogs. There is no definitive answer as to why they do it, but there are a few theories.

It could be a throw-back to their wild ancestry as an attempt to maximise food intake & digestion. I have also heard it suggested that as some wild animals eat their own faeces so as not to leave a scent for predators, this could be the reason. However, wild dogs are not, in general, prey animals so I discount that theory.

Dietary deficiency is another possibility (although there is very little evidence to support this as dogs on a good, balanced diet will also exhibit coprophagia).

Bitches clean up their puppies' faeces, so coprophagia could be linked to this. However, that would not explain why male dogs also do it.

A further suggestion is that it is a conditioning reflex based on toilet training. If a puppy is scolded for "having an accident" on the carpet, it may thereafter try to dispose of any future evidence.

Personally, I think they just like the taste.

[LeeE]

Vomit, being only partially digested, still has nutritional value.  Provided that you don't mind the taste, it's worth eating.

With poo, a lot depends on the type of animal that poo'd it.  Generally, because their digestion systems are not totally efficient, the poo from herbivores and omnivores still has some nutritional value.  On top of that, if the particular animal has any digestion problems that further reduce their digestive efficiency the poo could be well worth eating.  Human digestion is relatively very efficient, which is apparent from the small amount of time we have to spend eating compared with the amount of time we spend using up the energy thus gained and as a consequence our poo has very little nutritional value and is mostly toxic waste.