Imagine turning up to every meal excited and hungry only to get the same dried up pellet over and over again. Dog's traditional diets were meat and bones and you can do no better than these.
The dog food companies would like us to believe that their product is as good as raw food and bones but in reality it is full of additives which over time have a range of detrimental effects on dog health.
Let's treat with a diet change and also as if he has a tummy upset.
Go to your health food store and buy colloidal silver, acidophilus and slippery elm powder or tablets.
Give him 5 mls of the silver twice daily. This is a side-effect free antibiotic.
Give him the human dose of acidophilus and slippery elm tablets once daily. You can mix these into quality yoghurt to feed. These will replace important gut flora required to digest food and soothe and line any inflammation in an irritated gastro-intestinal tract.
I also recommend that you place your dog on a diet of raw meat and bones i.e. beef/mutton bones with meat on them or raw chicken necks and wings, mince; definitely no processed food and snacks. You can also add some freshly cooked or raw vegetables and oats or rice.
If your dog is not already on this type of diet, then I suggest that you introduce it slowly.
The following articles discuss the importance of diet in greater detail: