The action of eating one’s own feces is called coprophagia, a practice common in young dogs and puppies. While many dogs grow out of coprophagia as they get older, some continue the practice far into their senior years.
One possibility is that your dog isn’t absorbing enough nutrients in its diet. This doesn’t necessarily mean they have a poor diet. Instead, something is getting in the way of their nutrient absorption processes.
Another possibility is that your dog is practicing coprophagia for behavioral reasons rather than medical ones. This is the most common reason why puppies eat their own poop.
Where possible, go outside with your dog when they need to relieve themselves. Then you can pick up the feces straight away, eliminating any chance of your puppy eating poop that’s left lying around.
Grab some vinegar from your pantry (any kind will do) and douse your dog’s stool with it. When your dog inevitably licks the poop, he will despise the taste of the vinegar and stop immediately.