TJ Dunn Jr., Veterinarian
It’s well known, and generally accepted among experts, that dogs (and cats) are carnivores, and have evolved over eons as primarily carnivores. Though now “domesticated,” our pets haven’t developed a rumen along their digestive tract to ferment cellulose and other plant material, nor have their pancreases developed ways to secrete cellulase that breaks down cellulose into glucose molecules, making them efficient at helping dogs and cats digest, absorb, and utilize plant material as a high-quality protein source. Herbivores do that. That’s just how nature works at this point.
On the other hand, plant materials such as rice, soybean meal, and corn have some, albeit limited, utility in a carnivore’s diet. Corn, wheat, soybeans, rice, and barley are not bad or harmful to dogs or cats. These plant materials are simply not good choices as the basis of an optimally nourishing diet for current, past, and near-future carnivores (we get to choose what we feed our pets, right?).
What is the difference between a grain-based food and a meat-based food for pet dogs and cats? If you don’t believe that dogs and cats are primarily carnivores, click away now. You probably won’t believe what I’m about to tell you. Most of what follows is taken from two excellent references on small animal nutrition: Canine and Feline Nutrition by Case, Carey, and Hirakawa, and Small Animal Clinical Nutrition III By Lewis, Morris Jr. and Hand.
There are 22 alpha amino acids that mammals require for various metabolic and energetic activities. Dogs and cats can synthesize 12 of these, but the remaining 10 must be obtained from the diet. These 10 amino acids are called essential amino acids because they must be obtained exclusively from food (see the list in Table 1).
But the word “essential” is misleading, because all of these are vital for health. Long ago, some people called amino acids that the body cannot produce and that must be ingested “essential amino acids.” Who said the science was accurate?
Amino acids used by dogs and cats
“Non-essential” (not essential to the diet)
Alanine
Asparagine
Aspartic acid
Cysteine
Glutamic acid
Hydroxylysine
glycine
glutamine
Proline
Serine
Hydroxyproline
“Essential” (can only be obtained through diet)
Arginine
Histidine
Isoleucine
Methionine
Phenylalanine
Tryptophan
Threonine
Ballin
Leucine
lysine
Taurine (cat)
Herbivores are in the favor of having billions of microorganisms with their numerous stomachs and long digestive tracts to produce amino acids in great quantities. Our furry friends, with their relatively short and simple digestive tracts, cannot take advantage of microbial amino acid synthesis and therefore require pre-made (i.e., they cannot make it themselves) amino acids (in the form of larger protein molecules) to provide sufficient variety in the foods they ingest.
Keep in mind that cats have some special needs that dogs don’t, such as a dietary source of a beta-amino acid called taurine (see “Cats Are Different” for more information).
What’s in a “balanced” diet?
The necessary fats are easily available from both plant and animal sources and can be easily mixed into the diet. We all agree that linoleic acid and (in cats) arachidonic acid are necessary. (Linolenic acid is synthesized from linoleic acid in both dogs and cats.) High-quality fats are readily available, can be stabilized with vitamins E and C, and are fairly stable in price. That solves the problem of dietary fat. Nothing complicated.
Vitamins and minerals are inexpensive, well-documented, and easy to add to any food. No problem.
Carbohydrates serve dogs and cats as a quick-burning fuel for all kinds of muscular and metabolic activity. Cheap and easily produced carbohydrate sources include rice, corn, wheat, barley, and soy. Hmm… they seem to be what pet food manufacturers often use as the first choice for the foundation of their diets. Some argue that these plant-based products are also excellent sources of protein.
In their book on nutrition, Cary and Hirakawa list 17 different plant foods as sources of carbohydrates, including rice, corn, wheat, oats, barley, and alfalfa. In fact, experts say that one of the benefits of carbohydrates is that they are protein-sparing, meaning that animals will use cheaper carbohydrate sources for energy before utilizing more expensive (human ideas!) protein.
So, to get the carbohydrate benefits, add some plant material to your ideal food and don’t confuse anyone by suggesting (or, even worse, stating) that corn, rice, and wheat are the primary protein products. (The same authors list 19 pet food ingredients used as protein sources, but ground corn, wheat, rice, oats, barley, and alfalfa are not on that list.)
This solves the carbohydrate problem in their diet. I know they use some inexpensive grains, but they never use grains as the basis or main component of their diet. Also, as you know, dogs and cats do very well on a diet that is minimal in carbohydrates and high in fats and high-quality proteins. In this respect, dogs and cats are different from humans. Remember that not all aspects of human nutrition necessarily match up with dog and cat nutrition.
Having stated that proteins are readily available as an energy source for dogs and cats, and that carbohydrates are much less important than in human diet and metabolism, our focus should be on the protein content of the ideal diet. Since we know that 10 amino acids are required from dietary sources, it makes sense to choose a protein source that contains a complete spectrum of amino acids.
Corn is a strict no-no as a protein source because it contains only 4 of the 10 essential amino acids and no taurine. Additionally, nutrition experts don’t even include corn in their list of protein sources for pet foods. It’s on the carbohydrate list.
Dog and cat nutrition The list includes substances that provide protein, such as beef, chicken, eggs, fish, lamb, and meat by-products. (FYI…the Association of American Feed Control Officials’ definition of meat by-products for pet food does not include hair, skin, hooves, or feathers, but refers to organ meats such as liver, kidneys, stomach, heart, blood, and spleen.) Meat by-products are an excellent source of protein for carnivores.
So, to include a wide range of amino acids in your diet, you would choose eggs, or more precisely egg whites, which are the best source of protein for mammals. This substance has a wide amino acid profile and is highly digestible. In fact, egg whites are considered the standard by which other protein sources are measured. Other really good options are meat, poultry and fish.
Therefore, our custom diets for dogs (and cats) include vitamins and minerals, grains for readily available energy, the right amount and ratio of fat sources, and a high-quality meat source as the foundation.
Pet food manufacturers know how to make great meals like the ones we make. The problem is that they are expensive to produce, especially when they contain ingredients like eggs, beef, or fish. And to compete with other pet food manufacturers, the price of the pet food determines the basis (main ingredient) of the meal.
That’s where corn comes in… corn is cheap, it takes up a lot of space in the bag and in your pet’s stomach so it “fills you up,” it’s a good source of carbohydrates so it gives your pet energy, it has some amino acids so corn contributes to the total protein on the Guaranteed Analysis list, and it’s cheap and available in steady supply. So pet food manufacturers make corn meals, add “meat and bone meal” (which is cooked at least twice before being bagged and can have too much calcium) to “complete the amino acid profile” and add a few other calculated substances so that they can put a big “complete and balanced” label on their pet food.
Nature has ensured that when it comes to feeding dogs and cats, cheap pet foods made from cheap plant-based ingredients will always be a poor choice when trying to nourish a carnivore. Conversely, expensive substances like eggs, meat, poultry, and fish are much better choices when creating a diet suitable for a carnivore. Note: “expensive” and “cost” are human terms and have no bearing on what nature has set out as to what constitutes an ideal diet for a carnivore.
In all of the nutritional texts mentioned in this article, the authors repeatedly emphasize the importance of high-quality, nutritious, and easily digestible pet food products. Admittedly, these products are more expensive for the consumer than generic brands. We, as animal caregivers, have an obligation to our animals to stop choosing pet food based on price alone and to strongly prefer high-quality products.
Dogs (and cats) are more active and healthier when meat, poultry, lamb and fish are the basis of their diet. In other words, we should choose to feed our pets meat and condemn the nonsensical practice of feeding them like herbivores simply because it is cheaper.
according to Dog and cat nutritionpage 174:
“In general, high-quality animal proteins provide a better amino acid balance for pets compared to the amino acid balance provided by cereal proteins, which are not as balanced or readily available as high-quality animal proteins…”
“High quality” refers to meat, poultry and fish products made primarily from muscle and organ tissue, not “meat and bone meal.” Some animal-derived meals may not be considered high quality depending on how they are processed.
Several people have expressed concerns about feeding dogs and cats “high protein” diets. A variety of diseases, including epilepsy, hyperactivity, and kidney problems, have been blamed on “high protein” levels. When trying to find what level of protein content in a diet is “high,” we often come across a wide range of numbers. Nutritional experts do not agree on what level of protein content is “high” in a dog (or cat) diet.
The data showing that excess protein causes kidney damage was extrapolated from results obtained by feeding uremia-inducing levels of protein to laboratory animals with kidney failure. The early studies that asserted that protein was harmful to dog kidneys were based on studies done in rats – not even in dogs – and that study drove the pet food industry for years.
After all, there is a big difference between how rat kidneys (are rats carnivores?) metabolize protein and how dog kidneys process protein. I would be happy to see just one scientific experiment in a dog or cat that proves that a good quality, balanced, high protein diet damages normal kidneys.
The more I look into the world of pet food, the more I am amazed at how much we still have to learn. And much of what we learn is self-taught. Nutrition and pets is a fascinating subject, and one that is worthy of serious investigation.
reference:
image: Melissa Gray /Flickr
