Rickets is a condition characterized by increased bone flexibility and deformity resulting in lameness and seen in rapidly growing chicks. It is manifested as a thickened and poorly mineralized growth plate and poorly mineralized bone. It is caused by calcium, phosphorus and vitamin D deficiency or imbalance. In birds with severe rickets, the keels are crooked, the legs bowed, the long bones end are enlarged, the bones soft and rubbery and birds may show stiff legged gait.
Note that calcium and phosphorus ratios are central to rickets development and high dietary phosphorus content has a similar effect to low dietary calcium concentration.
Chondrodystrophy
Chondrodystrophy results in short thick and usually misshapen long bones and often apparent enlargement of hock joint. Displacement of gastrocnemius tendons may occur. Chondrodystrophy is a generalized disorder of the growth plate of long bones such that linear growth is impaired and appositional growth remains normal. It differs from rickets in that mineralization is not impaired. Manganese deficiency alone may result in chodrodystrophy. Deficiency of the following nutrients have been reported to contribute to chodrodystrophy. They are choline, niacin, vitamin E, biotin, folic acid and pyridoxine.
OSTEOPAENIA, OSTEOMALACIA AND OSTEOPOROSIS
Osteopaenia is a non-specified term used to describe a decrease in amount of bone tissue such as can result from osteomalacia and osteoporosis. In osteomalacia, there is defective mineralization while in osteoporosis, there is loss of bone substance associated with normal mineralization of bone matrix. Deficiency in mineralized bone or osteoporosis may be caused by bone loss due to estrogen activity associated with onset of lay, follicular activity and subsequent egg laying or may be precipitated by inadequate dietary calcium. Ostomalacia which is a defect in bone mineralization is a response to dietary insufficiency of calcium. Exercise and environmental factors such as increased cage size may result in small improvement in bone strength of laying hens.