Imagine a food so nutritionally complete, so packed with every type of vitamin and mineral required for healthy body function, that the need for dietary supplements didn't exist.

That's the marketing message behind many brands of commercially produced dog and cat food, say pet supplements manufacturers. "A lot of people believe the food they're feeding their animals is absolutely complete," says Laura Maddocks, chairman of Noah's Quest, a Laguna Niguel, Calif.-based producer of pet supplements.

However, some commercial pet foods are cooked and processed at high temperatures to sterilize ingredients that aren't human grade, including animal byproducts such as tendons or hooves and meat from diseased animals or from those that were euthanized with chemicals. Vital minerals, vitamins, fats and other nutrients can be literally baked out of the food, resulting in pet ailments ranging from itchy, dry skin to immune system disorders.

As pet owners become more aware of the limitations in Bowser's or Fluffy's food, they are increasingly turning to dietary supplements made exclusively for animals. In addition, growing numbers of Americans consider their pets to be family members and are just as likely to think about Lassie's sore joints as Timmy's sore throat when they visit the supplements aisle.

"Close to 60 percent of the customers in a natural foods store are pet owners," says Susan Weiss, president of Ark Natural Products for Pets in Naples, Fla. "That's an audience of people concerned about health that passes their influence on to others in their sphere."

The numbers back her up. According to figures from market research firm SPINS, pet supplements sales in natural products supermarkets jumped 20 percent from Nov. 28, 2002, to Nov. 29, 2003—from $2.8 million to $3.4 million.

But despite their increasing popularity, pet supplements varieties are limited. Most product lines are restricted to vitamins and condition-specific remedies such as arthritis treatments, coat conditioners, anxiety reducers and probiotics made solely for dogs and cats.

It's not that manufacturers couldn't formulate different types of animal supplements. "It's really a marketing issue," Weiss says. Not only are humans conditioned to think dog and cat foods are nutritionally complete, but they also can't ask their pets what types of dietary supplements they need. So they opt for products that produce observable physical changes in the animal, such as a shiny coat or a limp-free gait. "It's reverse Pavlovian conditioning," Weiss says. "Instead of the bell going off in the animal's head, the bell goes off in the human's head," after seeing a difference in a pet's appearance or health.

Here's a look at the various types of pet supplements and how they're formulated.

Arthritis and joint pain remedies. By far the best-selling pet supplement, these products contain glucosamine and chondroitin, the same ingredients in human supplements designed to ease troubled joints. "A lot of human products come from testing on animal trials, so we have a lot of data about what works for animals," says Maddocks of Noah's Quest. But you can't give your pet the same glucosamine supplement you take because of dosage. Pets weigh less, so they need substantially fewer milligrams of an active ingredient. The National Animal Supplement Council recommends 45 mg of glucosamine per kilogram of an animal's body weight. Joint pain supplements are designed mainly for dogs. Cats have a different skeletal system from dogs, with more elasticity and spring between the joints. These qualities not only contribute to cats' leaping abilities, but also ensure minimal joint problems. Other arthritis-fighting ingredients found in pet supplements include vitamin C, which builds collagen, and willow bark, which eases inflammation.

Vitamins. These are the next-best seller in the pet supplements market, and they take a variety of forms, ranging from enriched beef jerky to powders that can be sprinkled on food. Even if they come in tablet form, they usually contain liver, beef, garlic or fish oil as a primary ingredient to ensure that they taste good enough for the animal to be willing to ingest them. "Palatability and taste are very important," Maddocks says. "You can't tell a dog or cat, 'Take this; it's good for you.'" The idea behind a vitamin is to duplicate what a dog or cat in the wild would eat. Undomesticated dogs are foragers, so they eat grasses, plants and berries in addition to meat. "We have vitamins with greens, grass, barley, alfalfa juice, kelp, juniper berries, cranberries and enzymes," says Andi Brown, director of Palm Harbor, Fla.-based Halo, Purely for Pets. "[Such ingredients help] with digestion, purify the blood, strengthen the urinary tract, promote stamina and have antioxidants. I take the vitamins too."

Cats in the wild are more carnivorous than dogs, getting their greens from the intestines of animals they kill. Consequently, they need more protein than dogs do, so their supplements contain amino acids such as taurine, glutathione and cysteine. Brewer's yeast also contains protein and can be sprinkled on dog or cat food. Cats also tend to have urinary tract problems, which taurine and iodine can help prevent, says Leon Rosen, president of Dancing Paws, a Tustin, Calif.-based pet supplements manufacturer.

Rosen says vitamins for dogs and cats also should contain minerals such as potassium, iron, copper, selenium and zinc, as well as the antioxidant vitamins A, C and E to support the immune system.

Coat conditioners. Vegetable oils and products that contain omega-3 and -6 fatty acids, including the oleic acids and evening primrose, flaxseed and fish oils, provide fats that can reduce an animals' shedding, itching and dandruff, Brown says. Vitamin E and brewer's yeast are also found in coat conditioners.

Anxiety reducers. These are designed for pets that travel, whether it's across the continent on an airplane or across town to visit the vet. These supplements are formulated to reduce stress, separation anxiety and motion sickness. Just like human anxiety-alleviating supplements, they can contain St. John's wort, kava, valerian, melatonin and chamomile, but in lower dosages.

Natural Foods Merchandiser volume XXV/number 3/p. 102, 106