Influence of dietary calcium, cation-anion balance, genetics and age on the development of leg bone characteristics and leg bone abnormalities in broiler chicks

Leg bone development involves the further differentiation of chondrocytes, which must precede calcification, recruitment of osteoprogenitors, resorption and replacement of the calcified cartilage by bone. Research reported in this dissertation focused on longitudinal and appositional growth.; Rapid growth and economically important carcass traits have been major contributors to the financial success of commercial broiler companies. The first experiment was to compare the development of the tibia and femur of Ross 208, selected for marketing as broilers, and Ross 308, selected for marketing as roasters. Body weight changes accompanied skeletal differences. At 21 days, there were significant strain differences in bone length, but that of the tibia was carried through to 36 days. Changes relative to bones need to be further characterized, particularly in light of the current problems with lameness in growing birds and bone breakage during processing.; Calcium, phosphorus, vitamin D and chloride can all affect the development of leg bones. The second experiment was to determine how dietary calcium affected chondrogenesis. Growth plates from chicks fed 1.0% calcium were normal. Growth plates from chicks fed 0.8% calcium mostly had enlarged prehypertrophic zones, indicating tibial dyschondroplasia (TD). Chicks fed 0.6% calcium had enlarged proliferative zones or a combination of TD and rickets. Findings suggest the association between rickets and severe or moderate Ca deficiency. The excess of chloride likely interfered with chondrocyte calcium utilization.; Maintaining acid and base equilibrium appears to be critical for growth, development and optimum tissue health. This last experiment was to determine how dietary concentrations of calcium, NPP, vitamin D, potassium, KHCO ₃ and NH₄Cl, would affect acid-base balance and growth plate development. A diet with 1.0% calcium caused a higher plasma pH than a diet with 0.8% calcium. Chicks fed a diet with 0.8% calcium developed moderate to severe growth plate enlargement. The addition of KHCO₃ decreased growth plate problems slightly. The majority of chicks fed higher soybean meal content had enlarged growth plates. Chicks fed diets with the higher calcium content had the lowest urine pH. Experimental evidence did not indicate significant changes in the systemic pH.