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The Nutritional Aspects of Bone Composition




By T. J. Dunn, Jr., DVM


Raw bones have been a part of canines' diets for as long as they have been tracking, attacking and killing their prey -- far back into the early shadows of evolution. Today's canine house pets share almost exactly the same genetic determiners of anatomy and behavior as their long-distant predecessors.


When early man found out that the canine, if captured very early in life, could be trained to do man's bidding, the destiny of the canine was changed forever. Humans found ways to breed the canine companions for specific jobs, such as hauling, hunting or retrieving. And coat color became important when "modern" humans got interested in status symbols and prized possessions. Body size and shape became important because the humans who were hunting prey needed specific types of canines to assist in the hunt. One type of canine would be better suited to chase down elk and another body type would be best at digging rodents from their earthen dens. That's why, in the world of dogs, we have today all sorts of body types and sizes.


What didn't change, though, through all those centuries of breeding for specific body and coat types was the internal configuration and function of organ systems. The general pattern of teeth, stomach, intestines, kidneys, liver, heart and other mammalian organs stayed the same.


If you were to take a look at the internal organs of a Saint Bernard, a wolf, or a Chihuahua you'd see that they are arranged, shaped, and function in identical ways! With such differences in body size, color and shape it doesn't seem possible that they originated from a common ancestor and share the same internal anatomical and biochemical machinery.


Modern man has modified a number of characteristics of the canine. But there's one thing man has not altered: the basic nutrient requirements of the dog. Dogs need today essentially the same nutrients that their predecessors required eons ago. That is precisely why there has been so much notice given to the practice of feeding dogs (and cats, too!) raw meat and other unprocessed foods.




There arises the question of safety when feeding raw foods, too. The risk of infection from food-borne pathogens such as Salmonella and E.coli need to be understood. And the question of the need to feed whole, raw bones to dogs has yet to be answered to everyone's satisfaction. There are many proponents of feeding raw bones to dogs and the feeling is that the benefits gained from consuming raw bones far outweighs any perceived hazard of bone impaction or intestinal perforation. (See the this article for information on the hazards of feeding whole bones to dogs.)


Finely ground raw bone, on the other hand, presents no hazard of causing constipation, obstruction or penetration of the gastrointestinal tract. Also the finely ground bone should be present in appropriate amounts because too much can upset important ratios of other minerals.


Proponents of feeding whole bones to dogs (the contention is that COOKED bones are a safety hazard, RAW bones are not) state that there are great nutritional benefits derived from consuming raw bones. These nutritional benefits can actually be seen in the greatly enhanced health status of the dog when the dog is switched away from processed, dry food diets.


Raw bones, some contend, are an absolute necessity; dogs will not live a long and healthy life unless their diet contains raw bones. But is this contention based on facts? Is it the actual bone itself that provides all these nutritional benefits, or the attached soft tissues that really are the storehouses of nutrients? Let's find out where these nutritional benefits are really coming from ...



An Educated Look at the Nutritional Benefits of Bones


Marrow is not bone. In fact, the marrow cavity of any bone is composed mainly of fat and blood components -- high quality nutrients, to be sure, but the minimal reward for scraping out a bit of fatty marrow hardly warrants the status of it being declared a daily requirement for a dog. 


Bone marrow, according to the Official Publication of American Feed Control Officials, 1997,"...is the soft material coming from the center of large bones, such as leg bones. This material, which is predominantly fat, is separated from the bone material by mechanical separation."


Cartilage, meanwhile, is 50 percent collagen (a poorly digestible fibrous connective tissue) and mucopolysaccharides which are chains of glucose molecules in combination with mucous.


Are Whole Raw Bones a Requirement for Health in the Canine?


As a veterinarian with over thirty years of hands-on experience dealing with healthy and sick dogs and cats, and as a veterinarian with a keen interest in nutritional consequences affecting dogs and cats and as a member of a national veterinary nutrition association, I must ask two questions of those who so staunchly believe that RAW BONE consumption is an absolute requirement for dogs:


1. Could it be that the nutritional benefits seemingly derived from feeding RAW BONES is mostly derived from the meat, fat and connective tissues attached to those raw bones more so than from the actual bone itself? In other words, "Is the benefit really coming from bone ... or from the attached muscle, fat, and connective tissue?"


2. How can it be explained that I have seen many very healthy, old dogs in the course of practice that have never eaten a single RAW BONE? (Of course these old, healthy and very fortunate pets have owners who are feeding these dogs meat, fruit and other "table scraps". That may be precisely why they are old and healthy!)


Other questions I asked myself included: Are there lots of vitamins in bone? What is the protein value of bone?Are there lots of amino acids (the building blocks of protein)? Is the protein in bone of good quality... like in an egg white, or more like in leather? Is good quality fat present with Omega-3 and Omega-6 Fatty Acids? Besides Calcium is there an abundance of other minerals present? Are carbohydrates present as an energy source?


To help answer these questions myself, I did a little research, asking the question "What is bone made of?"  If whole RAW BONE is so absolutely necessary in a dog's diet the proof would be in the biochemical composition of the bones. Remember, I am referring to bone alone, without any meat, fat, or other connective tissue or blood attached.


Here is what I found and the references are included so that anyone can look up exactly the same information ...


(The data is analyzed on a DRY WEIGHT basis, that means the composition of bone is looked at as if there was no water present. Since water is not an actual nutrient -- although absolutely essential for life!-- and water is so abundant in most foods, nutritionists assess ingredients on a dry weight basis so that comparisons between different foods can be done without regard to the water content.)


Let us take a one pound raw thigh bone (with all the water vacuumed out) and see just what its ingredients are:


From Miller's Anatomy Of The Dog, 2nd Edition, W. B. Saunders Co., page 112: "Bone is about one third organic and two thirds inorganic material. The inorganic matrix of bone has a microcrystalline structure composed principally of calcium phosphate."


Bone, then, is composed mainly (two-thirds) of calcium phosphate. The calcium and phosphorus ratios and total amounts in the diet are very important factors, especially in rapidly growing, large breeds. The results of ongoing research clearly document that the unique nutritional needs of the large breed puppy are best provided by a diet matrix containing a minimum of 26% protein (high quality, animal-based source), a minimum of 14% fat, and 0.8% calcium and 0.67% phosphorus.


Also the ideal amount of calcium in the food is 1.0 to 1.8 percent of the dry weight of that food. Low quality dog foods often contain 2 and even 3 percent of the dry weight as calcium. This is due to the large amount of ground bone in the meat, poultry or fish meal. Diets with high amounts of "meat and bone meal" may surpass the optimal percentage of calcium.


I also drew data from Orthopaedics: Principles and Appications, Samuel L. Turek, M.D.,  J. B. Lippincott, 1985, 2nd Edition:


The Composition of Bone (Human)

(Technically this means substances that have no Carbon atom present.)
    65 to 70 percent of the bone is composed of inorganic substances.   Almost all of this inorganic substance is a compound called hydroxyapatite. [Think of this substance as little mineral crystals.]  The chemical composition of hydroxyapatite is (10 Calcium atoms, 6 Phosphorus atoms,  26 Oxygen atoms, and 2 Hydrogen atoms). 
    Therefore, 65 to 70 percent of bone is a mineral compound called hydroxyapatite that is composed of nothing more than Calcium, Phosphorus, Oxygen and Hydrogen.  There are no Vitamins, Fatty Acids, enzymes, proteins or carbohydrates in this, the largest component of raw bone.  It is a nice source of Calcium and Phosphorus, though.

(Technically this means substances that do have Carbon atoms present.)
     30 to 35% of bone is composed of organic material (on a dry weight basis).  Of this amount nearly 95 % is a substance called collagen. Collagen is a fibrous protein.  It is poorly digested by the dog and cat.  The other one-twentieth of the 30% organic substances are Chondroitin Sulfate, Keratin sulfate, and Phospholipids.
    Therefore, 30 to 35% of bone is collagen with a tiny fraction of other compounds.
     The following quote is from Canine and Feline Nutrition by Case, Carey and Hirakawa, 1995, page 175... "The matrix of bone is composed of the protein collagen. Collagen is very poorly digested by dogs and cats yet will be analyzed as protein in the pet food."


So, if we have a one pound bone (and all the water is vacuumed out) and we feed it to our dog for its wonderful nutritional benefits, where are those benefits coming from? If 70 percent of the bone is minerals and only 30 percent of that one pound is composed of poorly digested collagen, where is all this purported nutritional reward? There are no vitamins, no omega fatty acids in bone, no digestive enzymes, and only scant amounts of poorly digestible amino acids locked up in the collagen. Even if stomach acids could leach out all the collagen locked up in the bone fragments the collagen would yield minimal nutritional value.


Nevertheless, finely ground bone is a good source of calcium and phosphorus. Finely ground bone presents no risk whatsoever to the canine or feline digestive tract. Rather than feeding whole raw bones to dogs based on the erroneous notion that those whole bones provide outstanding nutritional benefits, we are much more accurate in asserting that whole raw bones provide a good balance of calcium and phosphorus for dogs... and that's about it! (For chewing exercise why not use a hard rawhide bone that softens if ingested?)


Image: Craig Howell / via Flickr



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