Calcium is the most abundant mineral in the body, making up nearly two percent of the pet’s total body weight. More than 99 percent of the calcium in the body is found in bones. Calcium is primarily used as a structural component of bones and teeth and also as a messenger that enables cells to respond to hormones and nerve transmitting chemicals. Many enzymes depend on calcium in order to work properly, as do the nerves, heart, and blood-clotting mechanisms. Calcium is absorbed from the diet in the intestinal tract under vitamin D regulation.

In people, supplemental calcium is most commonly prescribed for the treatment of osteoporosis and premenstrual syndrome (PMS). Other uses include colon polyps and cancer prevention, hypertension (high blood pressure), high cholesterol, preeclampsia, attention deficit disorder, migraine headaches, and periodontal disease. Calcium seems to work best when combined with vitamin D.

Supplemental calcium is available in a number of forms, including calcium carbonate, dolomite, oyster shell calcium, bonemeal, calcium citrate, calcium citrate malate, tricalcium phosphate, calcium lactate, calcium gluconate, calcium aspartate, calcium orotate, and calcium chelate. Calcium bicarbonate is the only form of calcium that can be ionized in the blood, but calcium bicarbonate is not stable when synthetically produced.

Calcium lactate is most easily converted in the body to calcium bicarbonate, and as a result it is the form preferred by many doctors. Recent studies have shown that calcium citrate is better absorbed than calcium carbonate and some other forms of calcium.

Sources of Calcium for Pets
Milk (or soy milk fortified with calcium), cheese, and other dairy products are excellent sources of calcium. Other sources of calcium include orange juice, fish canned with its bones (for example, sardines), dark green vegetables, nuts and seeds, and calcium-processed tofu.

Most pets get their calcium from bones in the diet or supplements added to the diet.

If calcium supplements are prescribed (as they are with most homemade diets), which one is best? There is no real good answer. Natural forms of supplements often come from bones, shells, or the earth (bonemeal, oyster shell, and dolomite). Bonemeal is often heated.

However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead. The lead concentration should always be less than two parts per million, although this is not often listed on the label.

Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating. Feeding it to the pet with meals improves absorption, because stomach acid is released to digest the food. Studies indicate calcium carbonate is not as well absorbed as calcium citrate.

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate).

The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

One advantage is chelated forms are well absorbed regardless of stomach acid. A disadvantage is chelated calcium is often more expensive than calcium carbonate. Furthermore, calcium may interfere with the absorption of chromium, iron, manganese, and magnesium. If these supplements are prescribed, it is best to administer them to the pet at a different time from when you administer the calcium supplement.

Therapeutic Uses For Calcium With Pets
Low blood calcium (hypocalcemia) can occur in pets eating an all-meat diet (meat is low in calcium; meat diets should be supplemented with bones or calcium supplements). The disease seen with low blood calcium as a result of improper diet is called nutritional secondary hyperparathyroidism. The condition is very rare in dogs and cats (except in those eating all meat, non-supplemented diets) and quite common in pet reptiles and birds (who are often fed the incorrect diet). Correcting the diet cures the disorder.

Dogs and cats with kidney failure can also develop a form of hypocalcemia called renal secondary hyperparathyroidism; calcium supplementation and/or efforts to lower blood phosphorus levels are indicated, as kidney failure cannot be cured.

Hypocalcemia also may occur in pets (predominantly small breed dogs) immediately before or shortly after giving birth (postpartum hypocalcemia). Intravenous calcium supplementation corrects the seizures seen in pets suffering from this disorder.

Pets suffering from pancreatitis may also show low blood calcium. High blood calcium (hypercalcemia) most commonly is seen in dogs and cats suffering from poisoning with vitamin D rodenticides (rodent poisons) or with cancers, especially lymphosarcoma and anal sac adenocarcinoma. High blood calcium levels in an otherwise normal pet should prompt the doctor to look for undiscovered cancers.

Dosages
The Association of American Feed Control Officials (AAFCO) recommendation is 320 mg/kg of body weight per day (puppies), 119 mg/kg of body weight per day (dogs), 400 mg/ kg of body weight per day (kittens), and 128 mg/kg of body weight per day (cats).

Safety Issues
In general, mild calcium supplementation is safe but is not necessary for most pets unless there are medical reasons to recommend supplementation (or unless the owner prepares the pet’s diet at home).

  • However, excess supplementation with calcium has been linked to skeletal problems (osteochondrosis) in large breed growing puppies.
  • Pets with cancer or parathyroid gland problems (hyperparathyroidism) should not receive calcium supplementation without veterinary supervision.
  • Extra calcium supplementation should also generally be avoided in pets with kidney or bladder stones composed of calcium oxalate crystals.
  • People taking corticosteroids, colchicine, isoniazid (INH), long-term sulfa antibiotics, heparin, aluminum hydroxide, digoxin, methotrexate, Dilantin (phenytoin), or phenobarbital may need more calcium. This may also apply to pets, although additional calcium supplementation is usually not prescribed.
  • Pets taking antibiotics in the tetracycline or quinolone (such as enrofloxacin, brand name Baytril) family should take prescribed calcium at a different time of day because calcium interferes with the medications’ absorption.
  • Pets taking thiazide diuretics, calcium-channel blockers, or atenolol should not receive extra calcium except under veterinary supervision.
  • Pets taking antacids (such as Zantac, active ingredient rantidine, or Prilosec, active ingredient omeprazole) may not be able to absorb calcium carbonate well and should receive a different type of calcium supplement.

Shawn Messonnier, DVM

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Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!

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