Calcium Carbonate

In the feline diet—as in the diet of most animals—calcium must be supplied in proper balance with phosphorus. Phosphorus occurs abundantly in meat, while calcium is largely found in bone. The natural benchmark for this balance is the calcium-to-phosphorus ratio found in adult wild mice, the cat’s primary ancestral prey. Research places this ratio at approximately 1.33 parts calcium to 1 part phosphorus.

Biological roles of calcium and phosphorus

Calcium is the most abundant mineral in the body, with 99% stored in bones. Around 70% of bone calcium is in the form of hydroxyapatite—a calcium phosphate mineral that gives bone its strength and rigidity. Hydroxyapatite is also the primary mineral component of tooth enamel. Beyond skeletal support, calcium plays a vital role in many physiological processes, including enzyme activity, muscle contraction, nerve transmission, heartbeat regulation, and blood clotting. When dietary calcium is insufficient, the body draws upon skeletal stores to maintain these essential functions.

Phosphorus is the second most abundant mineral in the body, with about 85% also located in the skeleton. The remainder supports numerous cellular functions, including energy metabolism, DNA and RNA synthesis, waste filtration in the kidneys, and regulation of other minerals such as vitamin D, iodine, magnesium, and zinc.

In nature, herbivores obtain calcium and phosphorus from plants, and in turn, supply carnivores with these minerals through their bones and soft tissues. For obligate carnivores like cats, prey provides both calcium and phosphorus in a naturally balanced and bioavailable form.

Balancing calcium and phosphorus in a raw meat diet

In formulating a raw diet for cats, it is essential to recreate not only the total quantity of calcium and phosphorus found in prey, but also their correct ratio. Pure meat—staple of raw diets—is high in phosphorus and low in calcium. Without correction, this imbalance can lead to calcium deficiency and related health problems.

While natural bone can be used to provide calcium, it also contributes additional phosphorus. Bone contains both minerals in a ratio of roughly 2 parts calcium to 1 part phosphorus. When feeding pure meat, balancing its high phosphorus content with only bone would would result in a diet excessively high in both calcium and phosphorus overall.

In prey animals like mice, not all tissue is meat or bone. Skin, fur, organs, and gastrointestinal contents add bulk and supply nutrients, but contribute relatively little phosphorus. Because these parts are not typically included in raw diets, the phosphorus concentration in homemade meals tends to be disproportionately high. To restore balance without exceeding safe mineral levels, an alternative source of pure calcium is needed.

Why use calcium carbonate?

To more precisely match the mineral content of natural prey and avoid over-supplementation, TCfeline includes calcium carbonate—a highly bioavailable and pure form of calcium that contains no phosphorus. This allows for accurate control of the calcium-to-phosphorus ratio in the final food, without contributing to excessive total mineral levels.

Source and purity

The calcium carbonate used in TCfeline is sourced from an exceptional geological deposit in the Mojave Desert of California. Formed over 300 million years ago, this deposit originated as a vast accumulation of marine animal remains—primarily shellfish similar to today’s oysters—laid down in a shallow sea. Over time, these remains were cemented together with precipitated calcium carbonate and subjected to natural metamorphic processes, including high pressure, geothermal heating, and mineral purification. Uplift and erosion eventually exposed the deposit, leaving behind an extraordinarily pure natural limestone.

This limestone is notable for its very low levels of lead and other heavy metals, making it suitable for both food and dietary supplement use. It meets the stringent requirements of California Proposition 65, which sets legal limits for lead in consumer products.

In summary

Calcium carbonate is included in the TCfeline premix to achieve a natural, prey-like calcium-to-phosphorus ratio—without the risks associated with excessive bone content. It provides a clean, bioavailable source of elemental calcium, supporting skeletal health, metabolic balance, and long-term feline wellbeing. As with all ingredients in TCfeline, its inclusion is based on both scientific insight and practical formulation experience.