12 year old golden retriever

Question
Why does my golden retriever eat other animals excrement. Is something lacking in his diet. It has got to the stage where he picks something up on a daily basis )Horse, sheep, cat or other dogs it doesn't matter what type). This is a bad habit we cannot get him to stop and is going worse as he gets older.

Answer
Why is poorly understood.  There is no successful history in changing chow.  I don't have any good ideas on stopping him.  There are additives you can put in their food to stop them from eating their own, but won't work for you.  all you can is try to reduce his access to them.  I fight the same thing when I take my old Lab to the woods.  She wants to clean up after the deer and rabbits.  

The only good thing I can say is that it is much harder on the owner's stomach than theirs.