Yeah, it happens for various reasons. The first thing to try is to feed pineapple. This has enzymes or acid (can't remember which) that helps break down protien in the diet so the pup can absorb. They eat the poo to get protien.
Make sure you just pick the poo up as soon as you can. The other reason is they see their mommy dog clean up after them when they are still with her.
Most times, the pineapple will help - takes several days though so don't give up too quickly
