Why is maintaining an exact calcium-to-available-phosphorus ratio of 2:1 critical in pullet starter feeds to prevent Tibial Dyschondroplasia (TD)?

Tibial Dyschondroplasia (TD) is a severe metabolic skeletal disease characterized by the presence of a non-vascularized, uncalcified plug of cartilage in the proximal growth plate of the tibiotarsus, leading to bone deformity, severe lameness, and high culling rates in young brown layer pullets. The primary nutritional trigger is an imbalance between dietary calcium and available phosphorus (aP). During the starter rearing phase (0 to 6 weeks), the skeletal growth rate is extremely high, and bone mineralization requires an exact, synchronized deposition of dicalcium phosphate. The biological ratio of calcium to available phosphorus must be kept strictly at 2.0:1.0 (typically 1.00% Ca to 0.50% aP). If available phosphorus is too high or calcium is deficient (disrupting the ratio to 1:1 or less), it stimulates the parathyroid hormone to resorb skeletal calcium, halting the blood vessel penetration into the hypertrophic zone of the growth cartilage. This vascular arrest prevents chondrocytes from calcifying, resulting in the retention of the cartilage plug (TD). Farmers can access bone histology guides in the Poultry Encyclopedia, buy premium feed grade calcium and phosphate sources on Poultry Plaza, track daily raw mineral rates on Poultry Rates, and trade healthy pullets on Murghi Mandi.