Making homemade dog food can be complicated. Animals have different nutritional needs than humans do. Bone meal can provide nutrients that help keep dogs healthy.
Bone meal is made from ground up bones. Bones and hooves from animals that have been slaughtered for food or industry are placed in a machine called a "bone crusher" and then are ground into smaller and smaller pieces. The coarser pieces are used in some industries, like the manufacturing of adhesives and gelatin. The smaller pieces can be used in dog food and as a plant fertilizer.
Bone meal used to be a standard ingredient in animal feed for all sorts of animals, including sheep, cows, pigs, cats and dogs. After the "Mad Cow Disease" outbreak of the 1980s, however, it's no longer included in livestock feed in many countries. Because cats and dogs aren't susceptible to "Mad Cow" disease (technically, bovine spongiform encephalopathy), bone meal is still legal for use in commercial dog foods, and offers nutrients that pets need.
Bone meal is rich in calcium, phosphorous, protein, and trace minerals. Phosphorous allows other nutrients to absorb into the bloodstream faster, and therefore, bone meal is especially useful for older dogs and dogs that may suffer from digestive disorders. It used to be common practice to sprinkle a little bone meal on a dog's food when it's suffering from diarrhea or "garbage gut" (which is bloating and flatulence when dogs over-indulge in human food or from eating garbage.) If you're making homemade dog food, you can simply sprinkle bone meal on each serving or add it to your mixture.
Making Bone Meal at Home
You can make your own bone meal at home by drying bones thoroughly and then grinding them in a spice grinder. Chicken bones, which are generally agreed to be too splintery for safe consumption, are rich in nutrients and grind up very nicely. You may want to chop the softened raw or cooked bones into small pieces so that they'll fit into your grinder better. Another technique is to boil the bones for a very long time, to render out the nutrients and then dehydrate the remaining liquid, grind that into a powder to use as you would commercially produced bone meal.
If you plan to purchase bone meal from the garden department, read the ingredients thoroughly because added fertilizers can kill your dog. Plants can tolerate chemicals and fertilizers that are added to bone meal, and often thrive when those are included, but dogs can become very sick if you feed them bone meal intended for plants. To find bone meal that's safe for animals, check your feed store, pet store, or online vendors that distribute bone meal for dog food.