Nutrition
As your Chihuahua ages, her nutritional needs change, too. Obviously, if your Chi is less active than she once was, she won't need the calories she required as a youngster. You can reduce your Chihuahua's caloric intake by either decreasing the amount of food she is fed on a daily basis, or you can keep the portion size the same but provide her with a reduced-calorie food.
Obesity is a huge problem among less active, older dogs. Every extra ounce on a Chihuahua places additional stress on worn out joints, as well as the Chi's heart. And, research indicates that overweight dogs are twice as likely to suffer from cancer as their more slender counterparts.
But caloric needs are not the only changes that an aging Chihuahua experiences and this is where meeting the Chihuahua's nutritional needs becomes more complex. Elderly dogs lose some of their ability to taste as well as their ability to metabolize food efficiently.
Addressing the Changing Palate
The commercial foods available today are made to be highly palatable or very appealing to dogs. In fact, many dogs find these foods so good that they overeat. With an older dog, however, the ability to taste what she is eating begins to dull. Suddenly the food she enjoyed eating previously isn't doing the trick for her anymore.
If you find that your Chihuahua is turning her nose up at what had been her favorite food, try revving up her appetite by increasing the smell of the food. Add a bit of something strong smelling and decidedly delectable, such as a little chicken broth or even a small amount of canned dog food.
Absorption Woes
Another change that senior dogs experience is decreased ability of their gastrointestinal tract to absorb important nutrients. Signs that your Chihuahua is not metabolizing her food well include increased stools, increased odor of stools, and weight loss. If your Chihuahua continues to eat a particular food that she can't metabolize, she can become malnourished.
If this is the case, talk to your veterinarian about alternative food choices. Some high-end, quality pet-food manufacturers have addressed this situation with foods specifically formulated for seniors. These foods contain higher concentrations of better quality nutrients in more easily digestible forms. Be sure to read labels carefully, as some foods packaged as senior products are actually weight-reduction formulas for seniors. Make sure you know what you are buying, as well as the quality and integrity of the manufacturer.

