Veterinary advice should be sought from your local veterinarian before applying any treatment or vaccine. Not sure who to use? Look up veterinarians who specialize in poultry using our directory listing. Find me a Vet

Calcium Deficiency


Calcium (Ca) is an essential mineral that is required for bone growth of chicks, egg shell formation in hens, muscle contraction, transmission of nerve impulses, and blood clotting. Calcium also acts as an important co-factor for several different enzymes and hormones.

There are many causes of calcium deficiency in chickens, even for birds that receive adequate amounts of dietary calcium in their daily diet. Dietary calcium can be reduced in chickens receiving:
  • Diets with too much phosphorus, such that it off balances the Ca:P ratio which should range from 1:1 to 2:1.
  • Foods high in oxalic acid (cassava, spinach, carrots, beet leaves, lettuce, sweet potatoes, turnips) which form insoluble calcium oxalates and decreases calcium availability.
  • Excess vitamin C
Several different vitamins and minerals interact with calcium, some act with calcium, and are required in order for the body to absorb it, and others act against it (antagonists).
calcium nutrient interactions

In order for chickens to be able to absorb calcium, they require adequate amounts of phosphorus (P) and vitamin D3. However they must all be in balance, as if birds are receiving excess amounts of P, it can decrease the chicken's ability to properly absorb Ca.

Calcium and phosphorus sources
Ingredient% Ca% P
Oyster shell38-
Calcium carbonate40-
Bone meal2613
Monocalcium phosphate1725
Dicalcium phosphate2120
Tricalcium phosphate2319
Defluorinated rock phosphate3419
Curaco phosphate3516
Phosphoric acid (75%)-25
Too much phosphorus can result in a condition known as secondary nutritional hyperparathyroidism. The ideal calcium to phosphorus ratio for chickens is 2:1.

Clinical Signs

Decreased egg production
Small eggs
Thin-shelled eggs
Skeletal deformities


  • History
  • Clinical signs
  • Diet analysis


Calcium: Oral supplementation of calcium in the diet or providing free choice calcium-rich options such as crushed oyster shells or limestone.


  • Feeding a balanced diet and providing additional calcium sources such as limestone or crushed oyster shells to laying hens.
  • Supplementing diet with psyllium may increase absorption of calcium

Scientific References

Risk Factors

  • Not receiving enough vitamin D and Phosphorus in diet
  • Diets heavy in grains (such as scratch), predisposes hens to inadequate calcium availability, and secondary reproductive disorders such as egg binding
  • Getting fed table scraps containing spinach or chard, which can potentially augment calcium availability issues in chicks and adult hens due to the presence of oxalates.