Notes on calcium and phosphorus

By Dr. Spencer Roach
Research and Development
Steve’s Real Food Inc.
Eugene, OR 97401

Raw diets, when prepared properly, are certainly the healthiest ways to feed dogs. But too often many people get confused about the proper ways to add calcium and phosphorus and change a great diet into a poor diet. Dogs need the proper amounts of calcium and phosphorus in order to grow well and remain healthy. This article will outline how much calcium and phosphorus dogs need, why, and will list the calcium and phosphorus sources of common ingredients used by many raw feeders.

Calcium and phosphorus are both essential minerals in canine diets. Calcium is a critical component of bone and cartilage, and it also plays a minor role in hormone transmission. Phosphorus is also a major component of bone. Calcium and phosphorus are found in bone as calcium hydroxyapatite, with a molecular formula of Ca₁₀(PO₄)₆(OH)₂. While the calcium/phosphorus ratio in hydroxyapatite is 1.7:1, energy-carrying molecules such as ATP (adenosine tri-phosphate) and others increase non-skeletal demand for phosphorus. As such, the optimal dietary calcium/phosphorus ratio is between 1.2:1 and 1.3:1. The chart below lists calcium/phosphorus minima and maxima for various life stages on a dry matter basis¹.

Calcium/phosphorus metabolism is mediated by 1,25(OH)2-vitamin D in the small intestine, and by parathyroid hormone in the bloodstream. There is a complex feedback loop that balances intestinal absorption, bone resorption, and renal excretion of both minerals. Too much calcium can result in increased bone density, which has been implicated as a factor in hip dysplasia in young and old dogs alike. Too little calcium can cause bone demineralization (and consequently an increased risk of skeletal fracture) and stunted growth. Phosphorus excess can lead to renal damage, while phosphorous deficiency is rarely (if ever) seen in carnivores.

Most of the calcium and phosphorus in Steve's Real Food chicken and turkey varieties comes from raw, ground up chicken backs or turkey necks. We also use a variety of calcium and phosphorus supplements in order to reach optimum levels of nutrition. Many raw diet advocates overestimate the levels of phosphorous in meat. Meat and pure calcium supplements alone do not provide adequate levels of phosphorus. We found through extensive nutrient analysis that we had to add phosphorus in conjunction with calcium. We use several pure calcium sources and calcium/ phosphorus sources to fine-tune our food's nutrition. Below are the calcium and phosphorus contents of some common raw meaty bones and other mineral sources. Also included are moisture, protein, and fat, so the mathematically inclined can estimate the dry matter calcium/phosphorus content as well as the energy density. Carbohydrate content is negligible for all ingredients.

1) Association of American Feed Control Officials (AAFCO), Official Publication, 2001.