By Ann-Marie Cole 2024
(Cert. Animal Nutrition, Dip. Canine Health & Nutrition, Dip Feline Studies, Cert. Holistic Health for Dogs)
Calcium is an essential macromineral needed by dogs and cats to grow and maintain strong bones and teeth, muscle contraction and nerve signaling in the body. When a deficiency occurs this can cause abnormal bone growth, demineralization of bone, secondary nutritional parathyroid disease, muscle twitching, appetite and energy reduction. Excess of calcium causes bone abnormalities.
Calcium has synergistic relationships with several other nutrients such as phosphorus, vitamin D, Vitamin K and magnesium in order to be absorbed and build strong bones, deficiencies in these nutrients will have direct impact on the available calcium and how the body utilizes it. For example, even if there is adequate calcium in the diet but vitamin D is deficient the individual can suffer from rickets, a softening of the bone as vitamin D is crucial in calcium absorption.
The recommended calcium intake according to NRC is:
Kittens: 2g/1000kcal
Adult Cats: 0.72g/1000kcal
Puppies: 3g/1000kcal
Adult Dogs: 1g/1000kcal
Dietary Sources: The best sources of calcium in a fresh food diet are raw soft edible meaty bones, calcium is also found in many other wholefoods such as dairy products, green leafy vegetables, almonds, sesame seeds, meat and organs, eggshells etc… Aside from bone and eggshells these will never come close to meeting a dog or cats nutritional requirements as plant sources have a low content and bioavailability as well as phytates and antinutreint and/or oxalates that will inhibit absorption. When using raw meaty bones the calcium content is variable among protein sources and cuts, as it’s a natural product there will always be natural variation. As a basic guide around 10% calculated bone content not including the meat portion it’s attached to is suitable for adult dogs and around 7% bone is usually going to provide adequate calcium levels for cats without causing constipation issues however these aren’t hard and fast rules, working with the animal in front of us is always important. Puppies and kittens need higher bone content amounts to meet their increased calcium needs, using formulated recipes at this time is best. Where possible working with typical calcium content data is ideal.
Supplement sources: Typically, in pet food we see calcium carbonate used in commercial products as it’s cheap and has a bioavailability of around 40% elemental calcium. This can also be used in fresh food diets where a non-food source needs to be used to provide calcium. Calcium carbonate can be derived from limestone and chalk and is also the calcium found in eggshells. Calcium Citrate can also be used, however has a elemental calcium content of around 21% but is thought to be around 25% greater bioavailability to calcium carbonate. Calcium carbonate like most calcium forms does require an acidic stomach to be optimally digested, whereas calcium citrate does not. Tricalcium Phosphate derived from rock is another that may be used in pet food with around 39% elemental calcium, classed as an inorganic phosphate this may impact kidney health and may be best avoided for animals with active kidney disease. When Calcium sources are used in pet feed as a ‘pure’ source such as calcium carbonate or citrate, phosphorus is often needed as another supplement to balance the calcium and phosphorus ratio if there isn’t enough present in the other ingredients. This is often in the form of an inorganic phosphate salt. Phosphate salts are also used for improved texture, palatability or as preservatives. Research is showing that phosphates are potentially harmful to the kidneys when consumed long term, this is especially true for cats. Pets who develop kidney disease need to have phosphorus and phosphate salts in particular reduced in the diet. Always look at pet food labels to see if there are phosphate salts added, it is best to avoid them even in healthy individuals.
Research in the human health space points to Microcrystalline Hydroxyapatite, the calcium found in bones to be a superior source of calcium not only to grow strong bones but to maintain bone density later in life. Its elemental calcium is around 20-25% but contains a host of other minerals such as phosphorus, zinc, copper, strontium and type 1 collagen required for bone formation and stimulates osteoblasts, cells responsible for new bone growth. Considering our carnivores evolved to eat bone matter it makes sense to assume that our dogs and cats likely benefit in the same way if not more so.
A study in Finland showed that puppies raised on a raw meaty bone based diet vs extruded or homecooked were at a reduced risk of developing hip dysplasia. This points to bone being a significant key in the formation of strong healthy bones and joints. Bone contains phosphorus, but a natural phosphorus that is less likely to impact the kidneys according the to study linked below. In cases where phosphorus needs to be restricted such as late stage kidney disease it may need to be re-evaluated in the diet and another calcium source that excludes phosphorus used.
As we can see not all calcium sources are created equal with various bioavailability’s and impacts on health. It’s important to always understand what type of calcium your pet is receiving and how it may affect their individual needs.
References and further reading:
1. Nutritional strategies for skeletal and cardiovascular health: hard bones, soft arteries, rather than vice versa. O’Keef et al. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4809188/
2. Calcium supplementation: the bare bones https://australianprescriber.tg.org.au/articles/calcium-supplementation-the-bare-bones.html
3. INFLUENCE OF NUTRITION AT YOUNG AGE ON CANINE HIP DYSPLASIA IN GERMAN
4. SHEPHERD DOGS: A CASE-CONTROL STUDY FROM FINLAND https://asiakas.kotisivukone.com/files/dogrisk.kotisivukone.com/INFLUENCE_OF_NUTRITION_AT_YOUNG_AGE.pdf
5. Effects of dietary phosphates from organic and inorganic sources on parameters of phosphorus homeostasis in healthy adult dogs https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7894875/
6. National Research Council 2006 Nutrient Requirements for Dogs and Cats
*Information on this website or article is not to replace that of a veterinarian.
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