That's coprophagia. They eat faeces due to lack of digestive enzymes or deficiency of some vitamins. Consult your vet and give him proper supplements.

you should consult with your vet to rule out health problems. stop the problem through training.. Have all the right materials for feeding, training, and walking your dog. Keep the dog’s living area clean, including the yard, so there will be no poops for him to pick up. Supervise your dog on walks, and pick up after him immediately. Work hard on the commands “leave it” and “come.” One simple exercise is to teach your dog to come to you for a food treat as soon as he has eliminated.

There are two reasons for such behaviour. 1. They like to keep their area clean. 2. If she lacks her nutrients or acids or enzymes or if it's not completely digested.

Thanks Dr Rohan for enlightening us with new info.

may b u r nt giving him enuf food..increase his food n then observe. my pup was duin the same..once I increased his feed he stopped duin it..