Here's more than you probably want to know about coprophagia.
1) In the short-term, if a dog is eating its own feces, coprophagia is both a normal and common canine behavior, and a harmless one. If the dog is ingesting the feces of other dogs or animals, it may run the risk of picking up a parasite or virus from the "donor." However, if the coprophagia is occurring among your own animals, there is little danger as long as you are keeping them healthy and providing the necessary vaccinations and heart worm medication. (The one exception may be young puppies that have not yet gained full immunity from parvo through vaccinations.) In the majority of cases, the behavior eventually stops on its own after a number of weeks or months. It is most commonly seen in pups between 4-9 months of age, who will most
...A) Everyone and her brother has a magic food ingredient that supposedly will prevent coprophagia, from pineapple to spinach to pickles--including all the commercial additives. Although some of these "supplements" seem to work for particular dogs, there is no certainty or guarantee that they will work for your dog. Statistically, most of the time food additives fail to stop the behavior. A behavioral reason for this, which the members of this list can appreciate, is that eating the feces is simply more reinforcing than the "nasty taste" is punishing. There is also a possible physiological reason for the failure of food additives. Dogs have survived is by developing a tolerance for what we would consider nasty tastes. As Nancy points out, dogs are scavengers and opportunists. (See the Coppingers' book, "Dogs," and their village dump theory.) Some studies suggest that dogs that engage in coprophagia, especially long-term, have an even more forgiving sense of taste than the average dog.
...) Although it was once thought that dietary deficiencies were a cause of coprophagia, most studies to date fail to show a clear or consistent correspondence between dietary deficiency and the unwanted behavior. Some dogs with nutritional deficiencies have ceased being coprophagic after their diet was improved, but as with the nasty tasting food additives, no particular nutrient seems to help all coprophagic dogs, and a majority of coprophagic dogs have no measurable deficiency. When a deficiency is associated with the behavior, it has most often turned out to be thiamin or one of a few trace minerals. So supplementation with a B-vitamin complex rich in thiamin may help some dogs. The link here is still tentative, though, because in a number of studies dogs that were deprived of nutrients did not become coprophagic. So while some coprophagic dogs have a nutritional deficiency, all dogs with deficiencies do not become coprophagic, and all dogs that are coprophagic do not have a nutritional deficiency.