You’ve heard it said, “variety is the spice of life.” That absolutely applies to what you feed your dog.
To illustrate, let’s imagine that someone invents a complete and balanced food for children. We’ll call it Tasty-Os. It has all the vitamins and minerals, proteins and fats – in the right proportions – that a child needs to grow. And they’re delicious … every kid loves Tasty-Os!
Pediatricians start recommending Tasty-Os for all their patients. Gosh, how simple that would make life for moms! There’s no need to supplement Tasty-Os with anything. In fact, you wouldn’t want to give your kid an apple, a piece of chicken or cheese, or a salad. That will cause a dietary imbalance!
Next, our enterprising Tasty-Os manufacturer comes out with something even better: complete and balanced Tasty-Os for every life stage: Infant, Youngster, Teen, Adult, and Senior. That’s right, everyone in your family can eat Tasty-Os and be certain they are getting all the nutrients they need. No more grocery shopping, just heat a bowl of Tasty-Os in the microwave! Set up your autoship online, and life is good! Or if you’re out and about, just go to the drive-through for some McTasty-Os!
Does that sound good? Easy? Reasonable?
Uh, no … it sounds absolutely insane!
But it also sounds familiar, doesn’t it? When veterinarians recommend a single food for a dog’s entire life, most people don’t question it, or wonder whether rotating dog food would be better.
Should Dogs Eat The Same Food Every Day?
Plain old common sense says animals ought to get a variety of foods. That’s true in the wild for every species, though one or two preferred foods may make up the bulk of the diet. Lynx, for instance, eat mostly snowshoe hares, but they won’t turn up their nose at other prey.
It’s certainly not like our dogs’ wolf ancestors seek only deer to eat. They hunt anything they can catch: elk, bison, moose, beavers, hares, rodents … even fish! They may also eat quite a bit of vegetation, like fruit, when it’s available
The veterinary literature is full of cases of nutritional deficiencies or toxic excesses. Almost every time, the problem arose (or was discovered) because the pet ate a single food for a long time.
Cats have most often been the unintended victims. Taurine, thiamine, copper, vitamin E and potassium deficiencies have occurred in cats fed one food as their sole diet. Dogs, whose omnivorous metabolism is more adaptable, haven’t had as many problems. But zinc and fatty acid deficiencies have arisen with certain poor-quality foods. Keep in mind, though, that all those foods met the nutritional standards in effect at the time.
Why “Complete And Balanced” Isn’t Guaranteed
But wait… how can a complete and balanced food cause such problems?
Even for the best of pet foods, there are several places where the food’s nutritional value can go astray before it gets to your dog’s bowl.
1. The AAFCO standards aren’t perfect. Pet nutrition is an evolving science, and we don’t know all there is to know about it (as if we ever will!). The particular nutritional needs of a species often become known through cases where they aren’t met. Cats have been on the short end of that stick more often than not (1, 2, 3). The AAFCO standards are designed to prevent deficiencies, not to achieve optimal health.
2. The individual nutrients in a given ingredient may be unknown or inaccurately stated. For plant ingredients, a batch might be presumed to have a certain nutritional composition based on previous analyses. But depending on weather, soil conditions, types of fertilizer, etc, the exact amounts of each nutrient may vary. Crops are less nutritious now than in decades past. Modern farming methods and agricultural chemicals deserve some of the blame. But many high-yield varieties grown today are just less nutritious (4).
3. Many suppliers contribute to each pet food. The big pet food companies have several manufacturing plants in the US as well as overseas. They often get ingredients from local suppliers. For example, Darling International owns many individual rendering plants. It supplies animal products to many pet food makers. Each is getting raw materials from local sources. Rendered meat and bone meal from a plant in Texas versus one in Oregon may be very different in quality and nutritional content.
4. Unknown ingredient quality. A vitamin-mineral premix purchased from an outside supplier may guarantee certain levels of each item. But if the quality control on that product was poor, the finished food will compound the error.
5. AAFCO profiles specify minimum levels, but no maximum limit for most nutrients. There is always the possibility that one or more nutrients may be excessive. Too much of some minerals may have adverse effects. For instance, crops grown in certain parts of the country have lots of selenium. Animal products where the animals eat local crops will have even more. A slight selenium overage in a mineral mixture may push the finished food to toxic levels.
Many nutrients degrade over time. Manufacturers need the food to meet its guaranteed analysis right up until its expiration date. This can be months to years in the future. Vitamins and minerals are therefore added at 300% to 400% over the required minimum level.
Manganese is one of the over-supplemented minerals. It has a very narrow safety range in humans. It may pose a health threat at levels far below than those found in many nutritional supplements. No similar studies have been done in dogs. But there is no maximum for manganese in any pet food.
6. Processing changes nutritional values. Dry dog food is subjected to heat four times during its manufacture; canned foods are heated twice. Heat processing alters many ingredients, some for the better and some for worse. Carbohydrates are made much more digestible by cooking. Proteins can be denatured, vitamins destroyed, and fats damaged by heat. Pet food manufacturers are aware of changes that occur during processing. They compensate for heat-sensitive ingredients by adding supplements. But alterations in proteins and fats are not necessarily accounted for.
7. The pet food manufacturer can make mistakes. This is one way that feeding the same food from the same manufacturer all the time can cause problems for your dog.
8. Variable nutritional needs. Consider all the different kinds of pet food on the market. When I started veterinary school, there were only two kinds: adult, and growth-pregnancy-lactation. “Light” foods were brand new. (It was a long time ago!)
Why Designer Diets Are Pointless
Now there are designer diets for tender tummies, itchy skin, excess pounds, specific sizes and breeds, a variety of lifestyles, and a few (largely fictional) life stages. (“All life stages” foods meet the standards for growth.) There’s also an wide array of “veterinary” diets.
What’s wrong with this picture? How different are these foods from one anther? They all meet the same nutritional standards: adult maintenance, or everything else. The ingredients and guaranteed analyses on the labels of regular and niche foods are similar, if not identical. The exact requirements of all breeds (and infinite combinations), every lifestyle, and each dog’s individual metabolism is unknown. Nor is it knowable … at least not with current technology.
Pet Food Recalls
The dreaded pet food recall seems to have become more frequent over the years. For kibble, aflatoxin (a poison made by certain mold) is one of the most dangerous causes. Hundreds of dogs have been sickened, and more than 100 killed, by aflatoxin. Moldy grain is expected to become a more common problem in coming years due to climate change.
Bacteria, particularly Salmonella, is a frequent cause of recalls, especially for commercial raw diets. The FDA has a “zero tolerance” policy for Salmonella that applies to all pet foods, but inspectors seem to target and test raw foods more often. Yet dry foods have caused more illness, especially in humans, from Salmonella contamination. Other common bacteria causing recalls are Listeria and Campylobacter.
More uncommon causes include formulation errors (too much or too little vitamin D), stray materials like fragments of plastic or metal, and in a few egregious cases, contamination with the euthanasia drug pentobarbital.
Variety is, once again, the best defense. If your dog isn’t eating just one food, the chance of harm from a recalled food is greatly reduced.
Food Allergies and Intolerances
Another pitfall of feeding a single food is the potential to develop an intolerance or allergy. A dietary intolerance is a reaction to something in the food. A food allergy is a reaction by the immune system. Both food allergies and intolerances can show up as symptoms in the digestive tract. But food allergies more often produce skin problems.
True food allergies are uncommon in pets. However, it’s finally occurring to veterinarians that most, if not all, cases of inflammatory bowel disease relate to diet (5).
The list of suspects is a long one. It includes flavorings, colorings, emulsifiers, humectants, stabilizers, thickeners, texturizers, preservatives, and dozens more. Different manufacturers use different additives. Rotating dog foods avoids chronic daily exposure to ingredients that could become a problem. If you’re still feeding dry food (despite reading this far), change it every few months. Try going from chicken-and-rice to beef-and-barley to rattlesnake-and-quinoa. (Yes, I’m making that one up!) With canned foods, you can change every day or even every meal.
Allergies are usually to proteins. Protein comes from animal products, of course. But legumes contain protein. Corn meal (“ground yellow corn”) is nine percent protein. Soybean flour contains 37 percent protein; wheat, 10 percent.
It usually takes months to years of exposure to a food to develop an allergy. People are surprised when Buster develops an allergy to a food he’s been eating for years. But that’s exactly when you should expect to see an allergy!
Some pet foods are produced on a “least cost” basis. For these, the ingredients may change from batch to batch. For instance, “meat by-products” may come from a cattle feedlot one week, and a hog slaughterhouse the next. “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 periodically change flavorings or other additives, resulting in rejection.
Habits and Tastes
The last big reason to rotate dog food often is to prevent finicky eating habits. Pet food makers are masters at making food tasty. While cats are more often labeled as finicky, dogs deserve the reputation as well. A dog fed a single food may reject anything else. Sometimes this is situational. Elvis, a Husky mix I often dog-sat for, loved his homemade food – except when traveling. Then he would touch nothing but plain McDonald’s hamburgers. He would have benefited from developing a broader palate!
When you buy a new can or bag, even of the same food, it could be different enough that your dog won’t eat it. What if you run out of her favorite food and you can’t get to the pet store right away … but you can get to the convenience store? Offering an unaccustomed food may cause strife (not to mention tummy upset)! If you board your dog, she may get fed whatever the kennel is using (even if you bring her own food, kennel staff can make mistakes).
It’s best that your dog be willing to eat whatever you give her.
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For all these reasons, I urge you to feed a wide variety of meats, food forms, brands, and flavors. Rotating dog food will help protect your dog. A problem with any one food is much less dangerous if you’re not feeding it exclusively.
- Dow SW, Fettman MJ, Smith KR, et al. Taurine depletion and cardiovascular disease in adult cats fed a potassium-depleted acidified diet. American Journal of Veterinary Research. 1992 Mar;53(3):402-5.
- Edinboro C, Scott-Moncrieff C, Janovitz E, et al. Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats. Journal of the American Veterinary Medical Association. 2004 Mar 15;224(6)879-886.Pion PD, Kittleson MD,
- Thomas WP, Skiles ML, Rogers QR. Clinical findings in cats with dilated cardiomyopathy and relationship of findings to taurine deficiency. Journal of the American Veterinary Medical Association. 1992 Jul 15;201(2):267-74.
- Davis MA, Hancock DD, Rice DH, et al. Feedstuffs as a vehicle of cattle exposure to Escherichia coli O157:H7 and Salmonella enterica. Veterinary Microbiology. 2003 Sep 1;95(3):199-210.
- A Glasgow et al. Role of Diet in the Health of the Feline Intestinal Tract and in Inflammatory Bowel Disease. Center for Companion Animal Health, School of Veterinary Medicine, UC Davis, May 2002.