Dogs mostly do this when they are suffering from malnutrition. If they are on a poor brand of dog food (cheap brands are made up of mostly corn, sprayed with flavor - no nutritional value) then their bodies crave protein, vitamins, etc. Without anything else to satisfy themselves they feel encouraged to eat their poop in hopes the second time around they might get something they missed. Not going to happen, but it's a vicious cycle. Change them to a better food & unless it's become a habit the behavior will stop.
What�s Really in Pet Food?
http://www.api4animals.org/facts.php?p=359&mor e=1
Just to mention too:
Illyria54, you have the name of EPI right, just out of order. It's actually called Exocrine Pancreatic Insufficiency (EPI) My male shepherd has this disease. However I wouldn't think of EPI in this case. Not unless soft, smelly (undigested food adds higher odor) yellow stools, loss of large amounts of fur (dog starts shedding very badly) & weight loss were also involved.
http://epi-research-fund.com/
cheers,
http://thegsd.info/