Sounds like Corgan's been hanging around with some cats! I wouldn't worry too, too much if he's not underweight. To encourage him to eat his dog food, though, you might try pouring a little chicken broth over it. You can make it easily and economically from chicken soup base that you get in the grocery store. It comes in plastic jars and is much easier to use than the old bouillion cubes. You can usually find it near the canned chicken broth. Just run some water in a bowl and spoon out a little of the stock, microwave it for a minute or so to get the water hot enough to dissolve it, maybe drop an ice cube into it so Corgan won't burn his tongue, pour it over his dog food, and see if he'll go for it. You could even keep a container of rice cooked up in the fridge and mix a spoonful in to make it even more familiar to his palate.
It makes really good soup, too! I used to make homemade chicken stock, simmering several pounds of skinned chicken thighs for hours and hours and hours, straining, finding room in the fridge, freezer, etc., etc., etc. . . regular Martha Stewart. (She'd have a coronary if she saw MY kitchen.) NO MORE. I pull out my trusty jar of Jamison's Chicken Stock and start cookin'! I use the ham stock instead of fatty ham hocks, and the beef stock is excellent, too. And, it's nice to be able to give my doggies a warm treat when they've been out playing in the cold. I'm just careful not to make it too concentrated, although it's not anywhere near as salty as the old bouillion or canned stock.