Biology, Physiology, and Dog Food?

Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution. Physiology is the branch of biology that studies the functions and mechanisms which work within a living system. You probably took biology in high school, and perhaps in college, depending on your major. As an undergraduate and veterinary student, I took not only basic biology, but also physiology, biochemistry, animal nutrition animal reproduction, anatomy, embryology, and more. In these courses I learned the details, the mechanisms, and the intricacies that enable animals’ bodies to function in so many diverse ways.

It is truly amazing to see how the body works — from the level of a single cell to a body system to the whole animal. Take the sheep, for example. She eats grass, weeds, anything she can find in a pasture. Depending on where she lives, she may get some grain, but it is a small part of her diet. The sheep converts grass and weeds into biological energy, which powers her basic body functions. That biological energy is also used for growth, producing wool, producing a lamb, milk production, and more. When you think about it, it is astounding that something as simple as grass can be converted into another animal, the raw material that becomes a sweater, or food that can nourish a lamb or complement a fine wine.

But what happens to the sheep if we take away grass and weeds? What if we fed her just grains? Simply put, she would weaken and probably suffer diseases of nutritional imbalance and lack. Her digestive tract is designed to process primarily fibrous plant material. While a sheep on pasture might eat some grains, it would be as the seed part of the whole plant, and would be a very small portion of her total diet.

By now you must be wondering how this relates to dogs. Lately, the issue of dogs, predominantly Golden Retrievers, that were fed grain-free kibble having an increased incidence of the heart disease called dilated cardiomyopathy (DCM). The issue is that these dogs have inadequate taurine levels, and taurine is essential for heart health. Taurine is an amino acid, a building block of protein. It is found in meats — some of the best sources are dark meat poultry, beef, venison, and some shellfish such as mussels and oysters. Today’s grain-free foods are being formulated with an increasing amount of legumes — peas, lentils, chick peas, and their by products, and the amount of protein coming from these ingredients is replacing protein that used to come from meat. Since plant protein contains little taurine, you can see that the amount of taurine in these kibbles could be lower than necessary.

Of course, it’s not all that simple, and we have much to learn about this problem. The genetic susceptibility of the individual, how effective digestion and absorption are, any interactions between other ingredients, amount fed, and other unknowns can explain why only some dogs who eat these foods are affected. But of course, owners feeding these foods, especially those who have Goldens, are very concerned. They are flocking to social media groups, posting ingredient lists, asking if this kibble is OK, if that one is bad, or of there is a kibble without peas, potatoes, lentils, and starch available. They’re calling their veterinarians, and getting varying answers about going back to dry foods that contain grains. They’re calling the manufacturers, and getting confusing answers, non-answers, and sometimes denial of the problem. It seems that all these owners want to is an answer to a simple question, “In the face of this taurine problem, what brand/formula/kibble should I feed my dog?”

Seems like a simple request, right? What kibble is best? The problem is, the wrong question is being asked. What owners really should be asking is,”What does the dog’s physiology require?

From a very basic standpoint, a dog needs water, protein, fat, vitamins and minerals, and a bit of fiber. Notice I did not mention carbohydrates (starches), as the dog has no dietary requirement for them. If we look at the dog’s nearest living relatives, the wolf and coyote, we know they eat a variety of prey animals, which consist of muscle meats, organs, fat, and bone. Ingesting hair of the prey and some vegetable content from the digestive tract provides fiber. They may also eat berries, fruits, or other vegetation at times. While many domestic dogs bear little physical resemblance to wolves, their DNA remains well over 99% the same. Their digestive tract remains similar to their wild relatives’, with sharp, shearing style teeth, a highly acidic stomach, and fast transit time.

Most kibbles are formulated with about 40% carbohydrates (starch). Some exceed 52%. Does that make sense, given the dog does not require carbohydrates? Would you feed yourself a food that was 40% starch (which digests to sugar) every meal, every day? Of course not! So why do companies continue to make foods this way? The simple answer is they need a way to make the food into the physical form of kibble. Some companies have figured out how to get the carbohydrate/starch level to¬† around 30%, but that’s still too high. My personal ideal is 5-10% carbohydrates for the average dog, and under 5% for the dog with health challenges including cancer, gastrointestinal disease, seizures, hypothyroidism, etc.

Thinking of these classes of nutrients, where should they come from? Water obviously is water, but the moisture contained in fresh foods also counts. Protein should be from meats, including red meats, poultry, and fish, to ensure a full range of amino acids. Fat comes with the meat, surrounding muscle groups or as the “marbling” we’re familiar with in steaks. It is also present in the marrow of bones. Minerals come from bone, as well as other organs and tissues. Vitamins are present in meats, organs, and plant materials.

Beyond where the required nutrients come from, it’s important to consider the form they are delivered in. We know that cooking denatures (damages) proteins, and in the case of taurine, may decrease the amount in a meat by up to 50%. Meat ingredients of kibbled foods may be subjected to three, and sometimes four, cooking processes. Fats are also affected by cooking, as bonds between the atoms they are made of are broken. Cooking makes fats harder to digest for the dog, placing an additional strain on the pancreas. Minerals and vitamins in kibbles are often in a chemical or synthetic form, which are not absorbed or utilized as effectively as the forms found in food.

Next, the quality of the ingredients should be considered. Did you know our meats and vegetables are graded? Meats that do not pass USDA inspection are typically sent to rendering plants to be made into meat meals. This includes “4D” meats, made from animals that are dead by means other than slaughter, down, diseased, or dying. That is one reason why no kibble can claim to be fit for human consumption (commonly called human quality). Grains and greens that do not pass can also be sold for pet foods, and have been blamed in recalls for both aflatoxins and salmonella.

Now that you are beginning to see that today’s dry kibble diets are inappropriate for dogs from a physiological vantage point, you are probably wondering what to feed your dog. There are several options beyond kibble! There are many fresh food options available, with protein coming from meat sources, a low or very low carbohydrate content. Some are cooked, some raw. Dehydrated base mix products are available, to which you add fresh meats. These can be advantageous in that you can choose the protein and the quality, and easily vary what you feed. Finally, you can make a home prepared diet, whether cooked or raw, with some guidance. It is crucial if you choose this option to know you are providing all required nutrients, either by following recipes that have been formulated to be complete, or by consulting a nutritionist. All of these options allow you to feed foods that are partially or totally fit for human consumption, a factor that is very important to me.


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