Do Dogs Need Variety in Their Diet?
Although they do like occasional treats, dogs, unlike humans, are content to eat the same food every day. So there's no real reason to make changes in a dog's diet to add variety. In fact, doing so may cause digestive upset and diarrhea. Not every dog has these problems, but many do when their food is changed.
There are times, Carreker says, when you do need to change a dog's diet. The two main times are when you go from puppy food to adult food, and then again when you switch from adult food to senior food.
When you do change food, it is best to make the change gradually by mixing the new food with the old. "Then," Carreker says, "over a period of one to two weeks, gradually increase the amount of new and reduce the amount of old until you're just feeding the new food to your dog."