No, this is not a line from a science fiction novel; it is just a way of calling attention to a very common myth among bird guardians: that of expecting indoor birds to get enough calcium by merely supplying them with cuttlebone, oyster shell or any other source of calcium that does not include vitamin D3.
Calcium is, by far, the most abundant mineral in vertebrate bodies. It is necessary not only for bone (and teeth) production but it’s also involved in sodium, potassium and magnesium balance; blood clotting; blood pressure; regulation of fluids and nutrients between cells; protein and fat digestion; nerve transmission; neuromuscular activity; vitamin B12 absorption; regulation of heart beat and the synthesis and metabolic effect of enzymes. No other mineral is more important for the body than calcium and both male and female birds need it but hens, especially during breeding season, need a higher dosage.
Calcium is a mineral acquired by the body from external sources, usually dietary ones. Of course, when one thinks of calcium rich foods, milk products immediately come to mind, but the problem with milk is that birds lack the necessaray enzymes for its digestion (only mammals have the capacity to feed their young milk from the mother's mammary glands). We, therefore, need to offer them vegetarian sources as well as cuttlebone. One thing to take into consideration is that calcium comes in two forms, carbonate and bicarbonate and, while vegetal sources are bicarbonated and easily absorbed, sources like cuttlebone or oyster shell are carbonated and more difficult to assimilate.
Foods rich in calcium
(*) Spinach, chard (both green and red), beet greens, soybeans, almonds and parsley are also rich in calcium but, at the same time, they are very high in oxalic acid which binds calcium and inhibits its absorption so they should never be fed to laying hens or birds with low calcium and, although they can be fed to healthy, non-breeding birds, care should be taken with the frequency and amount of offering.
But our birds can consume tons of calcium rich foods and still suffer from hypocalcemia (lack of calcium) if not enough vitamin D3 is present in the body. Vitamin D3 (also called cholecalciferol) is a steroid-like vitamin which main function is to allow the absorption of calcium into the system (it’s also necessary for the immune system, reduces inflammation, helps with cell proliferation and differentiation, and it’s directly involved in maintaining brain, skin, intestine and muscle cells health). This vitamin is not found in vegetal matter because it’s only produced by animal bodies from cholesterol exposed to medium wave ultra violet light. (UVB). Twenty minutes a day of exposure to sunshine is deemed to be enough to produce enough vitamin D3 (*) although it takes two days for cholesterol to become vitamin D3 as it needs to be processed by both the liver and the kidneys. Unfortunately, it’s very difficult to provide direct sunlight exposure on a daily basis to a captive bird, hence the necessity of supplements.
Symptoms of hypocalcemia (lack of calcium)
Incoordination to status epilepticus (seizures longer than 5 minutes or going from one convulsion to another without regaining consciousness)
Muscle cramping and weakness (falling of perches, staying at the bottom of the cage)
Tetany (tremors or twitches)
Eggs with thin/soft or no shell
Anxiety, restlessness or nervousness
Bone and heart disorders
But because D3 is a fat soluble vitamin that ends up stored in the liver and which cannot be eliminated by the body, if consumed in excess, it will cause calcium toxicity (hypercalcemia) which can be fatal. Therefore, one needs to be very careful not to oversupplement and a thorough evaluation of the bird’s needs, diet and environment should be done in order to determine whether supplementation is necessary and quantity and frequency of same. A word of caution: Pellets are usually fortified with both calcium and D3 and, again, care should be taken on the amount and frequency they are fed.
Symptoms of hypercalcemia (excess of calcium) and hypervitaminosis D (excess of vitamin D3)
Calcium deposits in soft tissue
Diarrhea or constipation and/or vomiting
Weakness/lethargy (falling off perches, staying at the bottom of cage, birds sleeps too much or level of activity decreases)
Itchy and/or dry/scaly skin
Loss of appetite
Retarded growth in babies
Kidney or heart damage
- Calcium is necessary for good health
- Calcium cannot be absorbed without Vitamin D3 already in the system
- Vitamin D3 is produced by the body through exposure to direct sunlight
- A lack of calcium and vitamin D3 is as serious as an excess of either or both.
- A thorough evaluation of the bird’s needs (species, breeding versus nosn-breeding, female versus male, environment) should be done prior supplementation.
(*) Please note that this exposure needs to be direct, ultra violet does not go through glass and only early in the morning or late in the afternoon. A bird should never be without shade when the sun is high. Also, there are no UV lamps manufactured for birds even though many are labeled and sold as such. All UV lamps in the market were created for reptiles and can burn the delicate cornea of a bird’s eye. And, although full spectrum lights do have a certain amount of UV, it’s not enough for vitamin D3 production.