Occurrence: Worldwide. Species affected: All, especially layers. Age affected: Young birds (rickets) and older, laying hens (osteomalacia or cage layer fatigue).

Causes: Deficiency of calcium in the diet caused by dietary variations in calcium and phosphorus content and bioavailability.

Effects: Soft, brittle bones (rickets) and retarded growth in young birds. In cage layer fatigue, eggs are thin-shelled or shell-less, there may be white areas on brown eggs or a drop in egg production and hatchability.

Vitamin D3 is needed for proper metabolism of calcium (Ca) and phosphorus (P), and in the formation of normal skeleton, hard beaks and claws, and strong eggshells. Rickets occurs in young birds and osteomalacia (cage layer fatigue) in mature birds.

A deficiency in the diet caused by variations in Ca and P content of animal byproducts and variation in P bioavailability in various mineral sources. A phosphorus deficiency is common in cage layers which don’t have excess to P in the faeces.

Soft brittle bones (rickets) occurs in young birds. In adults with cage layer fatigue, there are thin-shelled or shell-less eggs, white areas on brown eggs or a drop in egg production and hatchability.

In young birds with rickets, there is retarded growth.

Beaded ribs, deviated sternum, softening of the beak, claws and keel bone and skeletal distortions can occur.

Postmortem lesions and histopathology (widening of epiphyseal plat, hypertrophy and softening of the bone, and irregular patterns of cartilage and bone development in the primary and secondary spongiosa) are diagnostic.

It simulates other deforming leg weaknesses in poultry.

Quality control of the feed.

Restore proper levels to the diet.

Vitamin D3 is needed for absorption of Ca and P from intestine and deposition of calcium in bone. Ca and P are needed for bone growth. Deficiency in Ca or P, or imbalance of either will result in bone and egg shell malformations. Hyper amounts of Vitamin D may cause renal damage and pimpling of egg shells.

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