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The spice of life is variety, or so they say. If that's true for people, what about our dogs?

I love the commercial where the lady puts down a bowl of new dog food, and the dog shoves it under the rug. The voice-over intones, "(Our food), every day." It's very clever advertising, intended to put all of your pet food dollars into just one manufacturer's pocket. But the concept is all wrong.

For many of us, our animal companions are our children. So let's imagine for a moment that you actually have a child, let's say a 2-year old boy, and let's imagine taking him to the pediatrician for a check-up. The doctor bustles in, looks Junior over, then plunks a big can of Yummi-o's down on the exam table.

"Good news," he beams. "All the vitamins, minerals and a perfect balance of nutrients that Junior needs are right here in New Complete Yummi-o's. Now all you have to do is make sure Junior gets three servings every day." The doctor wags his finger at you as he continues in a serious voice, "Now, since this food is perfectly complete and balanced, you mustn't feed Junior anything else -– no apples or oatmeal or broccoli or peanut butter and jelly sandwiches –- because those might cause a nutrient imbalance!"

Well, this sounds a little weird, but you trust the pediatrician – after all, it's his name you see on all the gold-embossed university degrees on the exam-room wall – so you go ahead and put Junior on an all-Yummi-o's diet.

Time passes, Junior grows, and by golly, it sure is cheap, easy and convenient to feed him. The next year you bring him in for his checkup, and the doctor is very pleased.

"He looks great," says the doc. "I see you've been keeping him on Yummi-o's. Terrific! Now, I have more good news for you! Yummi-o's now comes in Life Stages! You'll keep him on Yummi-o's Growth until he starts kindergarten. Then he'll go on Elementary Yummi-o's until he hits middle school. Then you give him Adolescent Yummi-o's until he's 18, when he can be weaned onto the Adult formula. And it gets even better – you can eat it too! New Improved Yummi-o's is complete and balanced for adults up to 65 years old." Then he peers at you over his glasses. "Hmph," he says, "Well, maybe Yummi-o's Lite for you ...!"

Ridiculous? Of course! What rational parent would feed a child only one food for years on end? Even if the food is, in fact, complete and balanced, most of us would consider it unnatural, even cruel to the child. Never give Junior a cracker or a carrot? No fresh food at all? Preposterous!

Then why does everyone think it's okay to do it to a cat or dog? We would think a pediatrician who recommended a single food diet for a child was bonkers, yet when the veterinarian recommends a single food for our pampered puss, we obey without question. But feeding a dog or cat is not all that different from feeding a child.

It's way past time to bring a little common sense to bear, and common sense dictates that an animal ought to get a variety of foods.

The veterinary literature is full of cases where nutritional deficiencies (or excesses) were discovered, and in virtually every one, the problem arose (or was discovered) because the animal was kept on one food for a long period of time.

Cats, being strict obligate carnivores, have most often been the unintended victims – taurine, copper, vitamin E and potassium deficiencies have turned up in cats fed certain foods (which were, by the way, "complete and balanced" according to the standards at the time) as their sole diet.

Dogs, whose omnivorous metabolism is more adaptable, haven't had as many problems, though zinc and fatty acid deficiencies have occurred on certain poor quality foods. A zinc overdose in a commercial dog food sickened author Ann Martin's dogs and started her on a quest through the maze of pet food manufacturing and regulation, detailed in her stunning book Food Pets Die For in 1997.

The Myth of Complete and Balanced

Wait a minute ... aren't we indeed talking about "complete and balanced" foods? How can a complete and balanced food have deficiencies or excesses of nutrients? Unfortunately, even for the best commercial pet foods, there are several places along the road to the retail store shelf where the food's nutritional value can go astray.

Consider all the different kinds of pet food on the market. A few decades ago there were basically two kinds of pet food: adult, and puppy (growth/lactation); "light" foods were newly available and becoming ever more popular.

Looking at dog food today, we find all-life-stages food, puppy food, adult food, senior food, food for dogs with sensitive stomachs or sensitive skin, food for herding, sporting, toy, terrier, large, and giant breed dogs, vegetarian food, high performance food for working dogs, reduced calorie and light food for couch potato dogs, food for dogs with heart disease, kidney disease, liver disease, arthritis, digestive problems, cancer, diabetes, bladder stones, dandruff and dirty teeth.

However, the standards for pet food nutrient levels remain the same today as they were when they were set in 1989. There is one chart for adult maintenance, and one chart for growth/lactation. (Food intended to treat disease must provide documentation to FDA that it actually works as advertised, but the research is done by the company making the food -– and the claim.) New standards for dog and cat nutrition were just recently published by the National Research Council, but it will likely take several years before they are reviewed and accepted by AAFCO and pet food manufacturers must abide by them.

Is There Really a Difference?

Is it just me, or is something wrong with this picture? How much different are these foods really from each other –- given that they all have to meet the same nutritional standards? For instance, if you look at the ingredient statements on the labels of regular versus large breed foods, they look pretty similar. In any case, the exact nutritional requirements of hundreds of breeds (and infinite combinations of breeds), every imaginable lifestyle, and each animal's individual metabolism simply cannot be accurately known, at least not with current technology.

Moreover, even an individual animal's needs may fluctuate, depending on the season, his activity level, normal variations in hormone levels and organ functions, infections, parasites like fleas, illness, and a host of other factors. A dog who spends a lot of time outdoors in Québec may need a higher calorie/higher fat food in the winter to cope with the cold, but unless she is extremely active in warmer weather, such a food may put on the pounds if fed year-round. It does make a certain amount of sense to try to match the food to your animal's particular needs, although whether you can really do this based solely on a manufacturer's claims for its food is unlikely.

The Allergy Factor

Another pitfall of feeding a single food is the potential for your animal to develop an intolerance or allergy to one or more ingredients. A dietary intolerance is a reaction to something in the food, rather than the food itself.

The list of suspects is a long one and includes flavoring agents, coloring agents, emulsifiers, humectants, stabilizers, thickeners, texturizers, and dozens more. Different manufacturers use different additives, so changing foods periodically may avoid constant exposure to certain ingredients that could become a problem for your animal.

True food allergies are thought to be uncommon, but many practitioners and veterinary nutritionists are coming to the conclusion that most, if not all, cases of inflammatory bowel disease are linked to food.
It usually takes months to years of exposure to a food to develop an allergy. Allergies are usually to proteins, which are found in animal products, of course, but also in to some extent in the cereal grains commonly used in pet food. Corn meal (also known as ground yellow corn) contains 9 percent protein, soybean flour contains 37 percent protein, and wheat contains 10 percent protein. Corn and wheat are very common allergens in pets.

Switching foods every three or four months, from chicken-and-corn, to lamb-and-rice or turkey-and-barley or duck-and-green peas or rattlesnake-and-quinoa may help prevent your animal companion from becoming food-allergic in the first place. (But remember to carefully check the ingredient list on the package –- a food legitimately labeled "rattlesnake-and-quinoa" could actually consist mainly of corn and chicken.)

A Matter of Taste

The last big reason to change foods periodically is to prevent finicky eating habits. Pet food makers are masters at making the food irresistibly tasty. Consequently, an animal fed a single food may become "addicted" to it. I once got a call from a woman whose dog would not only eat just one flavor of dog food, but it had to have been canned at a particular factory! Cans of the same flavor with a different code stamp were rejected by the dog. She was frantically searching from coast to coast to find more cans from that factory –- which had since closed down.

Some foods are produced on a "least cost" basis, and the ingredients may change significantly from batch to batch. "Fixed formula" foods always use the same ingredients. Depending on ingredient quality, such a food may be a better pick. But even fixed formula foods that use the same ingredients all the time may still periodically alter certain characteristics, such as size of the kibble, or flavoring components.

When you buy a new bag of the same food, it could be just different enough from the usual fare that your furry friend will turn up her nose at it. Or you might run out of her favorite food and not be able to get over to the pet supply store right away –- she'll just have to eat something from the grocery store for a few days. If you board her, she may get fed whatever the kennel is using (errors can be made, even if you supply her own food).

It's best to have your animal companion develop more "cosmopolitan" tastes, and be willing to eat whatever you give her. (For dogs in some situations, training to accept food only from you can and should be done).

Time is on Your Side

For animals who have had food available day and night ("free choice"), the first step is to go to a timed meal schedule, where you leave the food out for an hour in the morning and again for an hour in the evening, but put it away the rest of the time. Believe me, your dog will not starve to death in 12 hours. The eat-fast-eat schedule is more natural to carnivores, and gives their tummies time to rest between meals. Also with this schedule, you don't have to worry about restricting the amounts you feed; the animal will eventually self-regulate very well on this schedule. The other big advantage of timed meals is that the pet will be hungry at meal time, and thus more willing to try new things. This is particularly critical when switching from dry to wet food with a finicky eater.

Easy Does It

When you decide to make the transition from one food to another, particularly dry food, be sure to plan ahead. You don't want to run completely out of one food and just slap down a bowl of something new in front of Fluffy's nose. He may not push it under the rug, but a sudden switch can cause tummy upset, which can lead to extremely unpleasant messes in the house!

If adding canned food or switching from dry to canned, this is also the time for an abundance of caution. The two forms of food are so vastly different, it will take some getting used to on the part of your pet's tummy.

Once canned food is a regular staple, it doesn't seem to be a problem to change flavors as often as every meal.

With dry food, for most dogs a four (or eight) day changeover works best. Young dogs usually adjust quickly; older dogs may need a little more time. For the first day (or two), feed 75 percent old food mixed with 25 percent new food. Then 50 percent each of old and new food, then 25 percent old food and 75 percent new food, and finally all new food. This gives the dog's resident gut bacteria time to gear up to handle the new ingredients properly.

Tummy Issues?

Many (if not most) animals will have a change in stool, even diarrhea, with a change of diet. As long as the animal is still eating well and acting fine, diarrhea is nothing to worry about; in fact, it's pretty normal, and will often persist for a week or two. (CAUTION: If your pet has additional symptoms, such as lethargy, poor appetite, or persistent vomiting, stop the new food and contact your veterinarian; there may be something else going on.) There are several ways to prevent or resolve diarrhea due to diet change:

Following Up

For the first two weeks after completing the changeover to the new food, closely monitor your animal's appetite, stool quality and energy level, and be alert for unusual symptoms -– itchiness, runny eyes, diarrhea -– that could be telling you the food is not right for him. (Of course, if you see problems earlier, stop the changeover and go back to the old food. Try another brand, or a more gradual switch.) Eventually, you'll be able to settle on three or four different foods you can use in rotation.

Remember, variety is critically important in your pet's diet. As tempting as it is to stick with one brand or recipe or flavor that your dog prefers, be sure to mix it up with different meats and veggies. This ensures that your pet is getting a good balance of nutrients, vitamins, and minerals.

As always, your companion's skin and coat quality, energy and activity level, and appetite are the best indicators of whether the food is compatible with his system and providing ample nutrition.