WEDNESDAY, March 30 (HealthDay News) -- Even though most Americans might believe that "senior" dog food is formulated differently than food for young adult dogs and pups, experts say that brands can vary widely in their ingredients and there are no requirements for what goes in foods for older canines.

A new survey finds that most Americans think that senior dog foods are lower in protein, sodium, fat and calories.

"But when we actually looked at the diets, there was an incredible range," said Dr. Lisa M. Freeman, co-author of a paper appearing in the latest issue of The International Journal for Applied Research in Veterinary Medicine.

The manufacturers "might be increasing protein, decreasing protein or keeping it the same," said Freeman, who is professor of nutrition at the Cummings School of Veterinary Medicine at Tufts University in North Grafton, Mass. "That emphasizes to us to look at the individual animal, and not all aging animals need a different diet. It's much, much more important to look at individual dogs."

The issue is close to home for many people, given that better medical care now allows many more pets to live longer lives.

The confusion stems from a variety of sources, one of which no doubt is the perception that there are minimum standards that must be met for dog food to qualify as "senior."

Although professional organizations do stipulate requirements for pups and adult dog food, the Association of American Feed Control Officials and the National Research Council have no such requirements for food marketed for aging or "mature" canines (beyond what's required for adult dog food).

Also, the term "old" is extremely relative in the canine world. The average lifespan for an Irish Wolfhound is only about six years but "a toy poodle at 7 is very young still," Freeman explained.

Some "old" dogs may be the picture of perfect health, while others might have a medical condition that warrants less sodium, for example, she said.

About 1,300 people -- 92 percent of them dog owners -- responded to Tufts University's web-based survey. Most respondents (84.5 percent) believed that senior dogs need to eat differently than younger dogs.

Although about 43 percent of Americans said they used a senior diet for their older pooches, only one-third had actually consulted their vet about it.

Respondents tended to assume that senior dog foods were lower in calories (in actuality, this varied from 246 to 408 calories a cup). And not all dogs gain weight as they age, Freeman said. Some lose and some stay the same, meaning calorie requirements may or may not change as dogs enter their golden years.

People also tended to assume that senior diets had less fat, protein and sodium but, again, this was not necessarily the case, with enormous variation among individual brands.

There is very little scientific evidence to suggest that dogs mimic humans as they age, though this is another widely held perception, the study authors stated.

"The study highlights the diversity among dogs and, consequently, dog food products. Each dog is unique and has distinct needs," said Kurt Gallagher, a spokesman for the Pet Food Institute, a trade group. "Attaining senior status depends on several factors, including the breed and weight of the dog. The differing nutritional needs of dogs are exemplified by the variance in the amount of protein senior dogs should consume."

"The study explains that some dogs require higher levels of protein from what they consumed earlier in life, while others actually need lower levels," Gallagher continued. "A variety of pet food products, including senior products, are available to pet owners so they may purchase a product that meets the specific needs of their pet. Dog owners may want to make a decision on whether to feed a senior diet, and which product to feed, in consultation with a veterinarian."

The study authors also advised talking with a veterinarian, noting that every "senior diet" for dogs is different and may or may not be appropriate for a particular dog, depending upon his overall condition and health.

More information

The American Veterinary Medical Association has more information on senior pets.