Most dogs enjoy white rice, which is easily substituted for dry food. Cats are less likely to enjoy a change in diet and are most often finicky eaters. Most cats however, do enjoy sprouts. Try mixing them with their regular food once per day. Most vitamins are low in calories and are flavored so that dogs are eager to take them from you.
Many pets naturally drink less as they age, which can lead to dehydration.
Try keeping several water bowls in different areas of the house to encourage your pet to lap it up. If you have a dog that doesn't get around much anymore, be sure to set a bowl close to her sleeping quarters. You can monitor how much water your pet is downing by measuring what's left in the bowls at night. Many aging pets lose some of the their hearing as they age, making them more vulnerable to accidents. Keep older pets confined indoors or on a leash when outside to prevent such occurences.