Your Jack is now considered a "senior". As they age, it is important that they have high quality protein to help with muscle maintenance. Dog food can get pretty pricey but if you are willing to spend the money, I would look for a high protein senior formula that is organic and grain free. We use Canidae dog food. However, there are plenty of other good brands out there. If you do transition your Jack to new food, remember to go slowly so you don't alarm his digestive system.