
All ways contact your vet if you are worried, we can't see your dog and we can't give veterinary advice only speak from our experience.
I would be weaning my dog back onto its normal food and not worrying able the mucus and blood smear but if you are worried then see the vet, there is no way we can tell how long this may go on but if the dogs stools are just smeared and he is not passing blood or lumps of congealed blood the problem would not bother me unless it continues for about 3 weeks.