Skeletal development in the meat-type chicken

1. This study ascertained how bone of modern meat-tl;pe chickens develops u nder typical commercial conditions and compares development with that in ge netic precursor stock. 2. A modern fast-growing selected strain and a slower-growing control strai n were used. Birds were weighed weekly A random sample was taken from each population at a range of ages up to 39 d. 3. A tibiotarsus from each bird was X-rayed and its dimensions and estimate d resistance to bending were determined. Cortical bone samples were ashed t o measure total mineral, calcium and phosphorus content. Cortical samples w ere also taken for porosity assessment. 4. As expected, the selected strain grew faster and heavier than the contro l strain. Despite this, both strains demonstrated similar periods of rapid bone formation (days 4 to 18) and mineralisation (days 4 to 11), and achiev ed similar estimates of resistance to bending. 5. However, cortical bone of the selected strain was less well mineralised and more porous than that of the control strain and showed a significant in crease in the molar Ca:P ratios above the expected range of values during t he first 2 to 3 weeks of life. 6. Despite production of bones with the correct dimensions for load support , the relatively poor density and mineral content of bone in the selected s train is likely to reduce effective breaking strength of the tibiotarsus. P ossible reasons may be either inadequate dietary supply of Ca and P or impa ired utilisation of the minerals due to a rapid growth rate or genetic fact ors.