CORVALLIS, Ore. - If Fido is getting a little long in the tooth or old Fluffy the Cat seems to be getting sick with increasing regularity, it may be that their immune system is deteriorating.

If so, it would behoove pet owners to pay special attention to the diet of their dogs and cats.

Increasing research on the links between nutrition and the immune system is revealing that many household pets - like their human counterparts - may be susceptible to immune dysfunction as they age, experts say, and that optimal nutrition can help retard or alleviate this process.

So if the family's favorite pet is entering its golden years - above the age of about eight to10 years for dogs and 10-12 years for cats - a little extra money spent or attention paid to their nutritional needs could help them age as gracefully and healthfully as possible.

"The best studies done on the relationship between nutrition and the immune system have so far been focused on humans," said Dr. Jean Hall, an assistant professor of veterinary medicine at Oregon State University. "But the more we learn about pets and other animals, the more similarities we are finding. It's increasingly clear that as pets age their immune response deteriorates, often in the same ways that humans do, and there are ways that an optimal diet can help."

Hall, who has published several professional papers in this field of study, says research shows aging is correlated to changes in the number of immune cells, their functional efficiency and other factors that affect their ability to maintain health and fight off disease.

Among the biological links observed between nutrition, health and the immune system:


  • Some dogs have been shown to have fewer white blood cells as they age, and other immune changes that appear linked to autoimmune disease and allergies.
  • Protein deficiency in animals can cause immune deficiency and lower resistance to infection.
  • Inadequate vitamin or trace mineral intake in various species has been linked to impaired antibody formation, lower immune response, and greater susceptibility to infection.
  • Obesity and consumption of diets high in fat can depress the immune system and increase the risk for serious infectious disease and cancer.

The reverse is also true, Hall said. Diets with proper balances of nutrients, vitamins and minerals, fed in the proper amounts, can go a long way toward preventing or alleviating many pet health problems.

The levels of fatty acids also appear to be a key, and pet foods supplemented with fish oils appear to help resolve some health problems, especially skin disease and arthritis.

"We have one advantage with our pets, of course, that we don't necessarily have with people," Hall said. "We can absolutely control what our dog or cat eats, which is more than you can say with a lot of human patients. And it may also be easier to get the dog to exercise than some couch-potato people."

So what's a concerned pet owner to do? Actually, Hall said, a lot of the research in this area is incomplete, and it's premature to make many recommendations about specific dietary regimens for certain diseases or health problems. And arbitrary supplementation with vitamins or other nutrients is probably unwise unless recommended by your veterinarian, she said.

However, feeding your pet a high quality diet is possible by paying a little more attention to the foods you purchase at the store, Hall said.

"The National Research Council has set up guidelines for pet foods that indicate whether they meet nutritional needs for gestation, lactation, growth, maintenance or all stages," she said. "That information should be available on pet food packaging or by contacting the manufacturer in writing."

But a key point to also consider, she said, is whether nutrient requirements were met by controlled feeding studies or simply by adding up the "minimum amounts" of each required nutrient.

"One study has pointed out that the presence of nutrients in a diet doesn't necessarily mean they can be readily absorbed and utilized," Hall said. "It suggested that a diet composed of shoe leather, motor oil, vitamins and minerals could meet nutrient recommendations for a dog or cat."

In the retail world, Hall said, there are four general categories of pet foods: generic, private label, popularly-advertised brands, and premium foods. The right research may find that any one of these can provide an adequate diet, she said, but generic and lower-cost brands often have not gone through rigorous, controlled feeding tests. They may also contain excess fats or nutrients.

Premium brands of pet foods emphasize optimal nutrition for health maintenance, longevity and performance, Hall said, rather than palatability and prevention of readily recognized nutritional deficiencies or excesses. Ingredients that do not contain too much of certain nutrients are used and the ingredients are not varied depending on their cost.

As a result, these foods are usually more expensive per unit of weight. But they are often higher in nutrient density and availability, which means less food is needed and can help offset the higher cost.

"I'd say if money is no object, buy a premium pet food that has probably gone through more rigorous testing protocols," Hall said. "It's likely you will be getting a product that will pay off in better health for the pet and a more functional immune system as they age."

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Dr. Jean Hall, 541-737-6537