Rickets is caused by a vitamin D deficiency or an imbalance in the Calcium / Phosphorus balance. It causes soft rubbery bones and beaks, usually seen in young birds. Grey partridges are particularly prone to this condition. Most commercial rations will have the correct amount of vitamins and minerals to prevent this issue. It is mainly seen when feed consumption or absorption is affected due to disease. Adding vitamin D to the drinking water can resolve the issue, but the underlying disease problem should be dealt with as well.