My feeling is that something is not going right for the poor chap.
What a dog food company thinks is appropriate for a canine may not be.
Clearly dogs are obligate carnivores and in their not too distant past would be consuming raw flesh of complete animals from the mouth to the anus. Yes, your wee pooch is a ravenous killer at heart.
When my dog is looking a bit down I go and buy a liver; pig or ox … I gently braise in water until the outisde is pink, leaving it rare inside and substitute that for one of her meals over a couple of days. The heating is just to kill any bacteria, without compromising all the good stuff.