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In human foods, bones have long been a staple for making ingredients like soup stock and gelatin; however, people don’t often eat bones directly. Rather, any bone that lands on our plates as a function of eating a steak, drumstick or chop often ends up being discarded or shared with the family pets.
While we are squeamish about such fare, few of our pets can resist the rich taste of the scant bits of meat and sinew clinging to the bone or the savory marrow inside. This is nothing new to the family dinner scene; this sort of behavior has been happening for the past 10,000 to 12,000 years.
In addition to these few leftovers, bone is also part of most every commercial dog and cat food sold today. Whether it is a component of rendered protein meal (e.g., meat and bone meal, chicken meal or fish meal) or in the mechanically separated or “emulsified” meats used in wet foods and treats, each contains measurable and intentional levels of bone. However, bone is inadvertently hidden to the petfood-buying public because it is not part of most ingredient names.
So, the perception that bone is a novel ingredient is understandable. The growing grassroots movements like raw (including Bones and Raw Food, or BARF) and home-prepared petfoods have increased awareness about bone in the diet and created some demand for bones (fresh, frozen, cooked and ground). More recently, with recall scares and concerns about low-cost micro-ingredients, some conventional petfood companies have also developed products that skip synthetic vitamins and minerals for more “natural” sources. In short, they depend on a significant amount of bone to meet many essential nutrient needs.
Most of the bones available are beef and pork and, to a lesser degree, lamb/mutton. Due to the nature of poultry processing, straight bones from chickens or turkeys usually wind up in rendered protein meals.
On the world stage, there are several forms of bone available. They are generally identified by regulatory agencies as:
F or petfood, fresh or frozen bones and steamed bone meal are the primary sources used. Fresh or frozen bones are commonly available at a butcher shop or the meat counter of the local grocery. A commercial-industrial trade in fresh or frozen bone is not well established.
Bones make up from 7% to 12% of beef or swine live weight. Age, body condition and feeding practices affect the composition of the bone. To wit, beef and pork bones will contain around 32-50% moisture, 20-29% protein, 12-22% fat and 13-29% ash (Ockerman and Hansen, 2000). Calcium composition of the ash is relatively constant at approximately 37.7%, regardless of age or species (cattle, pigs, sheep and poultry; Field et al., 1974).
Steamed bone meal is a light to dark gray granule or powder. It is sold with a guaranteed analysis for minimum calcium (~23-32%) and phosphorus (~13-15%). Suppliers may also guarantee minimum crude protein (~6-8%) and maximum moisture (~7-10%). The relative bioavailability of calcium in bone meal is equivalent to calcium carbonate (100%; Soares, 1995). Solubility and bioavailability of phosphorus is comparable to standard phosphate sources like mono-, di- and tri-calcium phosphate (Gillis et al., 1948; Gillis et al., 1954).
Steamed bone meal also contains measurable quantities of sodium (5.53%), iron (2.6%), magnesium (0.32%), potassium (0.18%) and zinc (0.1%; NRC, 1982). It can be a minor source of essential amino acids such as lysine and methionine (13.5% and 2.8% of crude protein, respectively; American Meat Institute, 1960). The fatty acids are derived primarily from bone marrow and contain more polyunsaturated fatty acids and phospholipids than intramuscular and subcutaneous fats (Ockerman and Hansen, 2000).
Much of the bone meal available for purchase in the ingredient market is imported into the US and other developed petfood regions. China, Pakistan and Thailand appear to be the leading marketers. Regardless of its origin, take care to verify that steamed bone meal does not exceed safe maximum limits for lead or other heavy metals. Further, one should purchase steamed bone meal through food or feed channels rather than fertilizer and garden supply stores to avoid potential cross-contamination with herbicides and pesticides.
From a safety aspect, bone has been cleared of implications in BSE. Apprehension about bone shards, splinters or chunks is often voiced, but according to people who market or feed raw petfood, this is apparently not an issue with raw bone. It should also be a non-issue with bone meal since the particle size has been reduced to a powder. In wet foods, the periodic sighting of bone bits is an appearance issue only because the bone has been reduced to gelatin and the ghost of the remaining minerals by the retort sterilization process.
So, in the end, bone can be a not-so-novel source of calcium, phosphorus and other nutrients in a pet’s diet.