Don't Let Calcium/Phosphorous Ratios Scare You

Don't Let Calcium/Phosphorous Ratios Scare You

It is widely known that cats have a dietary need for both calcium and phosphorous. Calcium is required by the body, not only for bones, but also for muscle control and ion balance. Phosphorous is important in the formation of bones and teeth, and also plays vital roles in cell membranes and energy processes.¹ Phosphorus is a structural part of cells; this is why meat tissue has high levels of it. Phosphorus is attracted to calcium, forming calcium phosphate, which is what gives bones and teeth their strength.
Just as important, and possibly even more so, is the ratio of calcium to phosphorous in the diet. Like big cats, the domestic cat's ancestral diet of whole prey would serve to provide the proper amounts of both of these minerals in the ideal ratio. This is because by weight, the cat's typical prey consist of about 7-10% bone.²
What is the ideal ratio and how can you ensure that your cats are getting proper amounts of calcium and phosphorous? Calcium to phosphorus ratios are typically written like this: 1.1:1, with the first number representing calcium and the second phosphorus. The ideal ratio of calcium to phosphorous in the feline diet is approximately 1.1:1. However, the ratio can vary from 0.9:1 up to 1.5:1 without any adverse consequences.³ Daily balance is not as vital as the overall balance over time, in weeks to months.
How can this ratio of calcium to phosphorous be achieved in addition to ensuring that your kitty gets adequate amounts of both of these vital minerals? The answer is simple. As mentioned previously, most prey species the cat would eat, such as mice, small birds and rabbits, consist of about 7-10% bone by weight and yield a ratio of about 1.1:1. Therefore, to achieve the proper calcium to phosphorous balance and properly mimic the ancestral diet, we can feed approximately 7-10% raw bones as part of the diet. We have provided a chart with the approximate weight percentages of bone for commonly fed bone-in cuts.
If you are making your own ground raw food, follow recipes to assure the correct calcium to phosphorus ratios. Alternatively, bone meal, dehydrated bone or eggshell calcium may be used in the appropriate amount. This will vary depending on the actual product and recipe used. Lastly, commercially available pre-made and pre-balanced raw diets are available for cats. Remember that each individual meal does not need to be in the correct ratio, rather, the ratio needs to be balanced over time. Feeding a meal of chicken necks, which have a bone percentage of about 36%, is fine as long as it is balanced by a meal or meals with a lower bone percentage.
Adequate amounts of and proper balance of these two vital nutrients is extremely important to your cat's health. Too little calcium in the diet can result in calcium being pulled from bones and may lead to fractures, weakness, and even seizures and death. Too much calcium can lead to growth problems or increased bone density leading to orthopedic issues. Too much or too little calcium can contribute to constipation. Inadequate phosphorous is extremely rare but can lead to hemolytic anemia and acid-base imbalance. Excess phosphorous is not known to be a problem except with cats with compromised kidney function.
Remember that daily balance is not as vital as long term balance. Feeding an improperly balanced diet for days to a few weeks is not likely to be a big problem unless you have a growing kitten. Beyond this time period, a lack of proper calcium to phosphorous balance is likely to result in health problems for your kitty. If you follow the recommendations above this should not be a concern for you.
Dr. Elisa Katz, DVM, is a graduate of Ohio State University and is the owner of Natural Pet Animal Hospital in Bourbonnais, Illinois. She practices holistic and integrative medicine focusing on proper diet and nutrition. Dr. Katz shares her home with four kitties and one dog.
  1. Michael S Hand, DVM, PhD; Craig D Thatcher, DVM, MS, PhD, Rebecca L Remillard, PhD, DVM, and Philip Roudebush, DVM, Small Animal Clinical Nutrition, 4th ed. Walsworth Publishing Company, 2000, 71-74.
  2. Ellen S. Dierenfeld, PhD, Heather L. Alcorn, BS and Krista L. Jacobsen, MS, "Nutrient Composition of Whole Vertebrate Prey (Excluding Fish) Fed in Zoos," U.S. Department of Agriculture, May 2002.
  3. Michael S Hand, DVM, PhD; Craig D Thatcher, DVM, MS, PhD, Rebecca L Remillard, PhD, DVM, and Philip Roudebush, DVM, Small Animal Clinical Nutrition, 4th ed. Walsworth Publishing Company, 2000, 310-311.
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