[Ellie May]

Coprophagia (poop eating) is usually thought to be behavioral because very few dog foods don't have enough supplementation. One medical exception to this rule is Pancreatic Enzyme Insufficiency. There are probably others also.

You could try changing foods though or add something like Deter. Some people have success with adding pineapple to the food of the pet whose poop gets eaten. Meat tenderizer can also work. If switching food doesn't work if you decide to go that way, it is probably behavioral and very common.