Older dogs have different dietary needs than their younger counterparts. If your dog is entering his golden years, make sure his food is formulated with optimal protein levels to help keep muscles strong. The food should also contain glucosamine, a compound found naturally in the body that helps cartilage for joint mobility.
Much of the issue of wet versus dry food comes down to your dog's preference. Older dogs sometimes have trouble chewing, however, and wet food is easier on their teeth and gums. If your dog has been eating dry food for years, he may not like the change at first; try mixing the wet and dry food together at first to ease the transition. Make sure the wet food is nutritionally complete, like Purina One wholesome entrees. Most importantly, introduce the wet food to your dog gradually, so that his digestive system has time to adjust to the dietary change.
Special thanks to Marc Morrone for sharing this information, and to Purina for giving a year's supply of Purina One Senior Care wet and dry food to our viewer mail participant.