As dogs age, changes occur in the way their bodies function, so it makes sense that what they eat also might need to change. The following list of health issues might be more common in aging pets.
Decreased Immune System Function
Throughout a dog’s life, a process called peroxidation occurs. Peroxidation is a normal process that the body uses to destroy cells that outlive their usefulness and to kill germs, parasites, etc. This process, however, also can destroy or damage healthy cells. As your dog ages, the damage caused by peroxidation accumulates, which, in turn, increases the risk of certain problems, such as infections.
 
Antioxidants are naturally occurring nutrients that help maintain overall health by neutralizing the peroxidation process of cellular molecules. Some antioxidants, such as vitamin E, beta-carotene, and lutein, are naturally occurring nutrients.
 
Recent research sponsored by The IAMS™ Company found that dogs fed a diet rich in antioxidants such as vitamin E, lutein, or beta-carotene had improved immune responses and vaccine recognition. This might be especially important in senior dog care; IAMS research has found that as dogs age, immune responses can decrease.
More Frequent Intestinal Problems
Older dogs might have higher numbers of unfavorable bacteria and lower numbers of beneficial bacteria in their intestines, which can result in clinical signs of gastrointestinal problems (e.g., diarrhea).
 
Feeding a diet containing fructooligosaccharides (FOS), a unique fiber source that helps nutritionally maintain healthy intestinal bacterial populations, promotes growth of beneficial bacteria. Beet pulp, a moderably fermentable fiber source, also helps maintain intestinal health by providing energy for the cells lining the intestine and promoting small, firm stools.
Different dogs show signs of aging at different times, and much of this variation is associated with size. Larger dogs generally appear 'old' sooner than smaller dogs. The table below lists the age at which various groups of dogs should be transitioned to senior foods, such as IAMS™ ProActive Health™ Senior Plus.
| Weight Range | Age to Begin Transition | 
|---|---|
| More than 90 lbs | 5 years | 
| 51 to 90 lbs | 6 years | 
| 21 to 50 lbs | 7 years | 
| Up to 20 lbs | 7 years | 
 
 Switching your dog to a new food takes some planning. Because dogs are creatures of habit, they tend to prefer their current food to a new food. Like us, they become accustomed to a food and might not be thrilled about a new routine. These useful dog-feeding tips will help you keep your dog satisfied.
When easing your dog into a change in diet, think “slow and steady.” Start by mixing 25% new food with 75% current food. Slowly change the proportions over the next three days or so by gradually increasing the new food and lessening the amount of the current food. Here’s a sample feeding schedule:
At the end of this weaning process, you should be feeding 100% of the new food. Your dog may want to eat only the old food, or not eat at all. Don’t worry — a healthy dog can miss meals for a day or two with no ill effects.
Bringing a new food into your home, pouring it into your dog’s bowl and declaring that he should eat it might cause your dog to go on a hunger strike. This is not the time to show who’s boss. It’s better to introduce the new food by using a pleasant tone of voice and gently encouraging him to try the new food.
Persistence is key! For the first two days of the food transition, don’t give your dog treats or table scraps. Dogs train us as much as we train them. Giving in to their demands only reinforces refusal behavior and makes it more difficult to make a nutritious dietary change.
Switching diets may be more challenging when changing from a moist food to a dry food. If your dog continues to resist eating dry food, mix in a little warm water. You might even want to put the moistened food in the microwave for a few seconds. If you mix the food with water, be sure to throw away the uneaten portion after 20 minutes to prevent spoilage. The same rule applies for canned and pouch food. After the dog has become accustomed to the moistened food, you can wean him onto completely dry food. To do this, follow the same mixing instructions outlined above.

