welcome to the not so nice world of puppy ownership. This activity is called cophragia and many many puppies do it. It's perfectly natural - just disgusting from our perspective - especially when they then want not just a little slurp but a full french tongues jobby - yeeeeeeeeuch.
Pineapple or courgette in the food is supposed to make the end product less appetising. I found the only way to win was to get there before they get to eat it which means cleaning up the second they do the poo. In a young puppy this is not a bad thing as you can reinforce the good behaviour of pooing but then a firm "no" if they go to eat it, but difficult if they're doing this when left.
Buddy used to do this - doesn't now though - but he has also pinched the odd bit of sheep and deer by product on occasion - sruffball that he is
The trouble is if you get one that's partial to any old type of poo:upchuckingsmiley:
good luck!