Hello Bill, I'm Dr. Deb.
I recently came online and see that your question about Lucy hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
This behavior is called coprophagia....the ingestion of one's own stool or the stool of another animal.
It's certainly a disgusting habit but it's actually a fairly common one, believe it or not.
We often don't have a good understanding of why some dogs engage in this behavior although it's rarely related to deficiencies in the diet.Many puppies go through an oral stage in which they explore everything with their mouths, sometimes ingesting a variety of non-food items, including feces.
As they mature, though, the majority of pups eventually learn that food tastes better than feces and that's the end of it.
But for those dogs who continue the practice (even if they start at an older age), there may be a compulsive component as to why they don't stop. It's almost an addiction, in a way. And, as a result, it's often very difficult to break this habit as it is for most compulsions.
There are products on the market designed to make the stool even more unappetizing such as Forbid or S.E.P. (stop eating poop). Some people will add Accent or meat tenderizer to the kibble. Some owners swear by fresh pineapple which is also added to the food.
Some people will try to sabotage the feces by adding jalapeno peppers or something really spicy to the stool.
I've had owners who tell me that at least one of these additives has been effective but, by no means, do they all find these products to be a solution to this problem.
Personally (and I do mean personally since I've had several dogs through the years who've done this and am currently living with one who does) the only thing that I've found that consistently works is to pick up the stool as soon as it's produced. If it's not there for a dog to ingest, then they don't ingest it.
You can also teach the "leave it" command which works if they start to eat the feces in front of you. This is a good command to learn anyway, in my opinion.
Of course, these methods will only work if you are present. For those times that you are not, you might consider fittingyour dog with a basket muzzle ( LINK)although I can understand why some owners would be reluctant to use such products. And, if the behavior is fairly intermittent, then this may not be a viable solution either.
If she only eats the other dog's stool (and not her own), you might separate them while you aren't home or consider crating one or both of them until you get the problem under control (depending on your living situation, the time they spend together and when Lucy has access to the other dog's stool).
I also encourage lots of exercise and quality time with their owners; boredom is not necessarily associated with this problem but it helps to rule it out by keeping the dogs active.
This can be an extremely difficult habit to break ....and a frustrating one to deal with as well....but I hope this helps and gives you other options to consider.
This is basically the equivalent of food poisoning so I try to discourage it as much as possible....not to mention how disgusting it is.
Again, my apologies for the delayed reply. Deb