Written by Laurie Goldstein, January 2014

Cat with mouse in mouth, croppedAs discussed in the article, ‘Dem Bones, ‘Dem Bones, ‘Dem… Scary Bones, there is no true substitute for fresh, whole bone-in meals in a raw fed cat’s diet. It’s not just about nutrition – chomping and crunching those pliable bones are extremely important for dental, digestive, and mental health.

What we ideally attempt to create when feeding raw is a food modeled on the perfect food for a cat – a mouse, rat, or rabbit. And mice, rats, and rabbits have bones from which our kitties derive many needed minerals, trace elements and other nutrients – not just calcium. And it’s a given that nutrients are best consumed in their natural, unprocessed form. Not only can processing damage them, but our increasing knowledge in the field of nutrition includes a broader understanding of the complex, synergistic nature of many nutrients, and the health benefits of consuming them in the same combinations and ratios as they naturally occur. The importance of providing nutrients in as natural a form as possible cannot be stressed enough; the more we deviate from that natural model, the more likely we are to be providing a less-than-optimal nutrient profile.

This highlights one of the biggest advantages of creating our own cat food over purchasing commercially processed products; we can control the extent to which nutrients are provided in their natural form. The closer we come to that objective – the closer we are to actually recreating a mouse – the less nutritional unknowns are a factor.

The ability to tailor the diet to specific needs is another important advantage of creating our own cat food. As important as it is to mimic the natural, there are times, in this less than ideal world, when we need a whole raw bone alternative, such as:

      – Transitioning to prey model raw

– Cats with no teeth or dental problems

– Cats with special medical needs, such as kidney disease / chronic renal failure

– Cats with impaired GI systems that make digesting and metabolizing whole bone difficult (at least initially).

Alternatives to fresh, whole bones for raw feeders include:

      – Ground bone

– Fresh bone alternatives:

– Freeze-dried bone: Microcrystalline Calcium Hydroxyapatite (MCHA)

– Eggshells (97% calcium carbonate)(1)

– Bone meal

Ground Bone

As close to natural as possible without being whole, feeding ground food is the first and best of your options. Due to the potential for oxidation of nutrients, however, ground food must be at least minimally supplemented. There are several time-tested recipes for ground food available, notably Dr. Lisa Pierson’s of CatInfo.org and that of Anne Jablonsky of CatNutrition.org.

Fresh Bone Alternatives

Calculating the Calcium: Phosphorus (Ca:P) Ratio

When substituting whole bone with powdered bone and alternatives, we can no longer use weight-based PMR bone feeding guidelines. Instead, we calculate a healthy calcium:phosphorus ratio (Ca:P) based on the amount of calcium and phosphorus in the bone product and in the meat and organs we use. The ideal Ca:P ratio for cats is between 1.0 and 1.5 parts elemental calcium for each 1.0 part of phosphorus.(2) To calculate the Ca:P ratio, the amount of elemental calcium in the product must be determined. Many calcium carbonate products list the amount of “calcium” in the product, but calcium carbonate is only 40% elemental calcium. If you choose to use a supplement not covered in this article, please ensure your calculation is based on the amount of elemental calcium in the product.

We are providing summary tables with this article indicating the Ca:P ratios of both MCHA and eggshell, along with various meats and organs. If you feed meats or organs that are not listed, you can refer to the USDA Nutrient Database(3) to determine the specific calcium and phosphorus amounts.

Bearing in mind that the ideal calcium-to-phosphorus ratio is in a range of 1.1:1 to 1.5:1, you will see in the tables that the calcium content doesn’t vary enough in meats or organs to need to micro-manage how much MCHA or eggshell to use, especially if you’re providing a variety of meats and organs over time (which you should be). And please note that although secreting organs typically contain 1.5x the phosphorus found in an equal amount of meat or muscle organ (heart, gizzards), the relative amount of secreting organ used in the overall diet is small, and our suggested amounts of MCHA or eggshell provide the targeted Ca:P ratios, over time.

Freeze-dried Bone: Microcrystalline Calcium Hydroxyapatite (MCHA)

MCHA is freeze-dried bone, usually from young cows pastured in Australia or New Zealand. It is the highest quality fresh bone replacement available because it is whole, uncooked bone; freeze drying retains nutrients virtually intact(4); and herd feeding standards in both Australia and New Zealand are superior to those in the U.S. Unfortunately, this tends to be an expensive option. When choosing an MCHA supplement, please ensure it has no other added ingredients. There is only one such supplement currently available in capsule form the U.S. It is marketed by NOW Foods, Inc., and is called simply “Calcium Hydroxyapatite.” Douglas Laboratories carries MCHA in tablet form, potentially appropriate for batches if you have the ability to grind the tablets and measure needed quantities. MCHA can be added to batches of ground food and frozen without nutritional impact on the supplement, or it can be sprinkled on individual meals when fed.

How Much MCHA do I Use?

If using 250mg MCHA capsules (the 250mg refers to the amount of elemental calcium in the NOW Foods product), to balance one pound of meat and organ (assuming a ratio of 90% meat, 5% liver, and 5% other secreting organ), 12.5 capsules are needed per pound. If adding on a “per meal” basis, between half a capsule and three-quarters (¾) of a capsule is needed per ounce for meat-only meals, and between three-quarters (¾) of a capsule and one full capsule should be used per ounce of meat plus organ meals. Please see Table 1, MCHA Ca:P Ratios with Sample Proteins and Organs, and choose the option with a Ca:P ratio you want to target.


In some cases, such as the need to lower phosphorus intake in cats with kidney failure, eggshells can be substituted entirely for bone. (There are other sources of calcium carbonate, including limestone and oyster shells, but eggshells are a far superior option and the only one discussed herein.)

Each type of fowl produces shells with slightly varying composition (and, as with all raw diets, rotation – even of your eggshell sources – is encouraged!). Obviously the diet of the chicken, duck, quail, etc. has an impact on the shell composition, particularly as regards trace minerals. That said, eggshells are an excellent bone substitute, as they are composed of similar minerals as bone, only with significantly less phosphorus and sodium.(5) This is what makes eggs the perfect bone substitute for cats requiring a low phosphorus diet, e.g. cats with kidney disease (CKD) or in chronic renal failure (CRF). Analysis of eggshells from varying breeds of chicken, duck and quail from around the world find underlying similarities – the primary mineral is calcium carbonate (ranging from 84% in quail eggs to 97% in chicken eggs), followed by small amounts of magnesium (from 0.2% in duck eggs, to 0.3% – 0.4% in chicken eggs), and trace amounts of sodium, potassium, zinc, manganese, iron, copper, boron, chromium, selenium, and vanadium.

**A Special Note on Using Eggshell Powder for Cats with Special Medical Needs, Specifically Kidney Disease or Chronic Renal Failure

Although restricting the phosphorus content in foods for kitties suffering CKD/CRF has been shown in studies to be very beneficial in protecting the kidney from further damage, it can be done without lowering the protein content (as was once the recommendation). And new studies have shown maintaining a high protein diet is crucial to the ongoing health of the cat.

A typical prey model raw meal is ~ 2.0% phosphorus on a dry matter basis. The prescription CKD/CRF foods target 0.5% phosphorus on a dry matter basis. Modifying a prey model raw diet (whether fed in PMR format or ground) by substituting eggshell for bone, the phosphorus load is reduced to about 0.8% on a dry matter basis. Depending on kitty’s kidney function, that switch to eggshell from bone may be more than sufficient to reduce the load on the kidneys to healthy function. The diet remains high in the B-vitamins that would otherwise need to be supplemented, and provides the high level of protein your cat needs to prevent muscle wasting. If this move alone does not help control the phosphorus excretion, up to 10% of the diet can be substituted with egg whites, raw or cooked. Egg whites provide high protein with NO phosphorus. This brings the phosphorus in the diet down to approximately the 0.5% (dry matter basis) targeted by the prescription diets, yet provides the cat with a species-appropriate diet that is easily digestible and highly bioavailable – a far cry from highly processed prescription kibble and canned products. The high moisture in this diet also helps keep kitty hydrated and all her organs (including those kidneys!) well lubricated.

For an excellent overview of feline kidney disease, please see Tanya’s Comprehensive Guide to Feline Chronic Kidney Disease: http://www.felinecrf.org/


How to Make Eggshell Powder

The best eggshells to use are those from organically, naturally raised, pastured animals. (In the U.S. “free range” does not mean they have access to a pasture.) You can see the difference in the yolk. In locally raised, pastured chickens, the yolk is a deep orange color (similar to the eggs I helped gather on my grandfather’s farm). Compare this to the pale yellow yolks of regular supermarket eggs. With traditional supermarket eggs, your cat will be getting the calcium she needs, but not the same range of trace minerals.

If you eat (or feed) eggs, providing eggshell powder to your cat is easy and economical. Save the shells, rinse away any remaining white. Keep the membrane (it provides glucosamine and chondroitin, good for joint health). Dry them: Place them on a plate in the hot sun for a few days to a week, or place them in the oven at 300^ for 10 or 15 minutes, or bake them at 200^ for 30 minutes. Tip: Put the shells in the oven to dry when you’re preheating to bake something else, or after you’ve cooked something on high heat.(6)

When the shells are brittle and crumbly to the touch, they’re ready for the (clean) coffee grinder. You’ll likely have to “pulse” it several times. The goal is to grind them as finely as possible, the approximate consistency of baking powder. Let them rest in the grinder for 15 or 20 minutes before opening it or you’ll have a cloud of eggshell dust puff out. Store the eggshell powder in an air-tight glass jar so it remains dry. One medium-large egg will produce roughly one teaspoon of eggshell powder.

In the U.S. you can also order finely ground eggshell powder from the e-shop at http://www.knowwhatyoufeed.com/shop_online.html

How Much Eggshell Powder do I Use?

Typically, 97% of the egg shell consists of calcium carbonate. To balance phosphorus with calcium, as discussed above, when calculating Ca:P ratios, it is the elemental calcium that matters. Calcium carbonate is 40% elemental calcium.

One teaspoon of eggshell powder (finely ground) weighs 6.1g.
The eggshell is 97% calcium carbonate.
Calcium carbonate is 40% elemental calcium.

X 97% calcium carbonate
= 5.93g of calcium carbonate
X 40% elemental calcium
= 2.37g of elemental calcium per teaspoon
(2,366.8mg of elemental calcium per teaspoon)
X 1/2 teaspoon
= 1,183.4mg elemental calcium per 1/2 teaspoon in eggshell powder

As an example, one pound of food consisting of 90% chicken thigh, 5% chicken liver, and 5% beef kidney, according to the USDA database, will have 763.2mg of phosphorus in the thigh; 67.2mg of phosphorus in the chicken liver, and 58.40mg of phosphorus in the beef kidney. It will have 43.2mg of calcium in the chicken thigh; 1.60mg of calcium in the chicken liver; and 3.2mg of calcium in the beef kidney.

The totals:

Phosphorus: Chicken thigh, 763.2mg + chicken liver, 67.2mg + beef kidney, 58.4mg = 888.8mg
Elemental Calcium: Chicken thigh, 43.2mg + chicken liver, 1.6mg + beef kidney, 3.2mg PLUS eggshell with 1,183.4mg of elemental calcium = 1,231.4mg of elemental calcium.

1,231.4mg elemental calcium divided by 888.8mg phosphorus = 1.39 Ca:P ratio using one-half teaspoon of eggshell powder. Obviously by rounding down a touch, or using a bit more organ, you can reduce the Ca:P ratio to 1.1:1 or 1.2.1. Please refer to Table 2, Eggshell Ca:P Ratios with Sample Proteins and Organs, and choose the option with a Ca:P ratio you want to target.

For a prey model raw diet, one-half (½) teaspoon of eggshell powder is needed per pound of meat and organ. To convert to per ounce, simply divide one-half (½) teaspoon by 16 (as there are 16 ounces per pound). This means it takes 1/32 teaspoon of eggshell powder to balance one ounce of food. Adjust as necessary per meal size.

Bone Meal

We do not recommend commercial bone meal be used as a bone replacement due to the concerns about bone meal’s high lead content and possible elevated mercury levels.(7) Bone meal is produced from defatted, dried animal bones, typically of older animals. If you choose to use a commercial bone meal, please purchase a human quality supplement with no other additives. Use the information on the content of phosphorus and elemental calcium in the product combined with the amount of calcium and phosphorus in the meat and organs you will use to determine the correct amount of bone meal to produce a healthy Ca:P ratio.

Homemade bone meal is a potential option. You can make your own bone meal with the bone-in meats you purchase. Use the prey model raw feeding guidelines of 82 – 84% meat / 6% – 8% bone / 5% liver / 5% other secreting organ. With that amount of fresh bone as the starting point (for the PMR weights), add just enough water to cover the bones and either use a pressure cooker, slow cooker, or slow boil to cook the bones until they are complete mush – basically just the collagen left in the structure. Once cool, run the very mushy bones through a food processor or blender with the liquid from the cooking process) and ensure that they are as finely ground as possible. IMPORTANT NOTE: Almost all the minerals leech out of the bones into the broth, so it is essential that the bone broth be included with the meal along with the food-processed mush bones. This method is not ideal, but is an option for those without a grinder who still desire to utilize fresh bone.

Of course, the typical recommendation is to *never* feed cooked bones. This is important: Cooked bones splinter into sharp pieces, and can cause serious internal damage that sometimes cannot be repaired. With this method, however, the bones become small crumbles (if done properly) and do not present that splintering risk.


In conclusion, there are several options when it becomes necessary to modify the whole bone content of your raw-fed cat’s diet, including replacing it altogether. So whether you’re transitioning a GI-compromised cat that can’t yet handle whole bone, dealing with a toothless kitty, or adjusting for a recently received CRF diagnosis, feeding your beloved feline the foods she’s meant to eat – the most nutritious and easily digestible diet possible – is within reach.

Table 1: Ca-P Ratios with MCHA (freeze dried bone)

Table 2: Ca-P Ratios with Eggshell



1. Dr. Peter Hunton, Calcium Sources for Laying Hens, Poultry Industry Council of Canada, Factsheet #133.

2. Know What You Feed: FAQ

3. This database is updated periodically. As of the writing of this article, the current release is SR25, September 2012.

4. NutritionData.com, Nutritional Effects of Food Processing.

5. Butcher, GD and Miles RD. Concepts of Eggshell Quality, Poultry Science Department, University of Florida, Gainesville, pub Alachua Free Network (AFN.org).; Shen, TF and Chen WL 2003. The Role of Magnesium and Calcium in Eggshell Formation in Tsaiya Ducks and Leghorn Hens, Asian-Aust J. Anim. Sci. 16(2): 290-296.

6. Thanks to Holisticat for the discussion on the use of eggshell as bone substitute.

8. Brigham and Women’s Hospital Encyclopedia.


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Created 01/19/14; Updated 08/11/14