A large amount of phosphorus is from the meat itself and although ground bone, as a source of calcium, is financially attractive, we have chosen a mixture of inorganic calcium/phosphorus minerals in the interest of the life-long health of the dogs. This ensures the calcium/phosphorus balance in the food and absorption and, as a result, biological availability in accordance with the daily needs of both pups and full-grown dogs.
The calcium/phosphorus balance in bone is always hard to determine, and even more so when the ground bone is included in the meal. There is a reason wolves do not chew/gnaw/eat the bones until the stomach is almost empty again. Wolves gnaw on bones after their meal and never during.
To free calcium from bone, the pH level (degree of acidity) in the stomach has to be low to such an extent that the calcium in the bone can be dissolved by the gastric juice. Only then can the calcium (and the phosphorus) be absorbed in the intestinal canal and is it available for the metabolism.
When there is a full meal in the stomach the pH level in the stomach is so high that calcium from bone dissolves either incompletely or not at all, making the availability of calcium and phosphorus from that source an uncertain factor.
That is why we have chosen not to use ground bone in Farm Food; after all food is the main, daily recurring factor where the health of your dog is concerned.
A Farm Food Rawhide bone or Farm Food Antler (made from naturally shed red deer Antlers) every now and then is fine, but only after the meal.