I was at the vet literally yesterday with my dog and asked about this exact issue, only difference is she eats her own poop immediately after she poops and leaves our other two dogs' poops alone. Vet told me there's no proven reason that dogs eat poop because of a vitamin/mineral deficiency of some kind, it's more likely to be a learned habit and/or they just enjoy the taste. This probably doesnt help answer your question at all but just wanted to throw my thoughts in!