Why does a high dietary level of calcium (> 4.5%) in pre-lay pullets cause urolithiasis and visceral gout?

During the rearing phase (0 to 15 weeks), a pullet's kidneys are still developing, and her reproductive tract is completely inactive. At this stage, her dietary calcium requirement is extremely low, around 0.8% to 1.0% of the feed. If a farmer prematurely feeds a high-calcium layer diet (which contains 4.0% to 4.5% calcium) to immature pullets, the excess calcium is absorbed into the bloodstream. Since the bird has no shell gland active to utilize this calcium, the kidneys are forced to excrete the entire massive calcium load in the urine. Because poultry urine is naturally rich in uric acid, the high concentration of calcium and uric acid in the renal tubules leads to the chemical precipitation of calcium sodium urate crystals (urolithiasis or kidney stones). These stones physically block the ureters, causing severe kidney swelling, renal parenchyma destruction, and kidney failure. Uric acid then accumulates in the blood and deposits as a chalky white powder over the heart, liver, and abdominal organs (visceral gout), leading to high mortality. Switching to pre-lay feed (exactly 2.5% Ca) only when the comb begins to redden is vital. Farmers can read renal pathology in the Poultry Encyclopedia, buy organic urinary acidifiers on Poultry Plaza, monitor daily feed rates on Poultry Rates, and list healthy pullets on Murghi Mandi.