Sometimes, in fact, pets may be sold short by more "natural" and healthful-seeming options. A January review of five raw dog and cat food diets in the Canadian Veterinary Journal — two commercial and three homemade — found that three out of the five were low in calcium and phosphorus and two were deficient in potassium, magnesium and zinc. The authors concluded that raw food may hypothetically be a nutritional risk for pets (though better studies are needed) and that it may also pose a risk of infectious disease to both pets and people.
But other times, paying more dough may pay off for a pet. A 2002 study in the American Journal of Veterinary Research compared meat meal to less-expensive corn gluten meal (a byproduct of corn milling that is a common ingredient in major pet food brands) as a protein source in dry cat food. After feeding the different foods to eight healthy adult cats (evenly split between males and females) then analyzing their urine, the researchers found that meat meal was more digestible than gluten meal, and absorption and retention of nitrogen, calcium, phosphorus and magnesium were better with meat protein too.
But just as is the case for organic foods for people, specialty pet foods are not immune to recalls due to contamination with E. coli or salmonella. In February, for example, the FDA announced that Texas-based Merrick Pet Care (makers of minimally processed, preservative-free pet foods) issued a recall of a pet treat because of potential salmonella contamination (no animals were reported ill).
And buyers should beware when reading labels — just as they should in the grocery store. Just because a pet food markets itself as "grain free" or "byproduct free" doesn't necessarily mean it will make a difference to an animal's health, says Dr. Jennifer Larsen, a veterinarian and professor of clinical nutrition at UC Davis.
"Food doesn't have to prove health benefits," she says. "Unless an individual pet has a specific documented intolerance to a certain type of grain, there's no advantage."
Furthermore, a "grain-free" food isn't necessarily higher in protein, Larsen adds. "It can still contain ingredients such as tapioca and peas. Often those diets are simply high in fat."
In some cases, vets say, there are legitimate reasons to choose specialty foods, such as meeting the nutritional needs of old age or treating allergies.
Celiac disease, which causes gluten intolerance, is present more often in certain dog breeds, such as Irish setters. And vets generally agree that some dogs and cats can have intolerances for certain grains such as wheat and corn; this can cause diarrhea or vomiting, and pet owners may not always recognize the cause.
How does a pet owner filter though all this information? Since every animal is different, experimentation may be in order to find the right food, says Scanlan, the holistic vet. "But just because something should be good for them doesn't mean it is. There is no such thing as 'the' best diet."
Instead of trusting pet store employees, Scanlan suggests owners talk to their vet, learn to read pet food labels and check out studies in peer-reviewed journals. And should they want to upgrade their pet's food but find they just can't afford to, they shouldn't feel guilty.
"Feeding them [a common brand] is better than dumping them on the street," she says. "You give them the best care you can."