Why is feeding a pre-lay diet (2.5% calcium) mandatory for exactly 10 to 14 days before the onset of lay in brown pullets?

The transition from a growing pullet to a laying hen represents a massive physiological shift. A grower diet contains only 1.0% calcium, which is insufficient to build the medullary bone reservoir. However, if a farmer immediately switches the flock to a high-calcium layer diet (around 4.0% Ca) before the ovaries are active, the pullet's kidneys cannot excrete the massive excess calcium. This leads to visceral gout, urolithiasis (kidney stones), and permanent renal damage. To bridge this gap, a pre-lay diet containing exactly 2.5% calcium must be fed starting at 15 to 16 weeks of age (or 10 to 14 days before the predicted first egg). Under the influence of rising estrogen levels, this intermediate calcium level is absorbed and directed exclusively toward the rapid deposition of medullary bone inside the femur and tibia marrow cavities. This ensures the pullet enters lay with a fully loaded calcium reservoir, preventing early osteoporosis while protecting her kidneys. Farmers can read endocrinology guides in the Poultry Encyclopedia, buy high-uniformity pre-lay feeds on Poultry Plaza, monitor daily rates on Poultry Rates, and trade laying pullets on Murghi Mandi.