As already suggested, I would change his food to a grain free brand like Orijen or Acana Provincial (www.championpetfoods.com
) as grains are hard for a dog to digest. And, plain
yogurt which only contain milk ingredients and bacterial cultures is great to add to help digestion.
Also, make sure you are not overfeeding him ....you have to take into consideration the number of treats he gets per day too. As SibHuskyMom mentioned, the guidelines on the bags tend to be overstated.