Causes of Rickets Rickets in humans’ chickens and every other animal that gets rickets is caused by a deficiency of Vitamin D3, phosphorus, or imbalance between Calcium and Phosphorus. Of all these, a deficiency of Vitamin D3 is the most common, and that is often secondary to bad feed that has been depleted of fat-soluble vitamins including Vitamin D. Ultimately, rickets usually occurs due to improper nutrition which results in poor skeletal calcification. Signs and Symptoms In chickens, rickets typically causes soft and pliable or rubbery bones and beaks that appear deformed. You can see this and other clinical signs