Changes in dimensions and mechanical properties of bone in chicks fed high levels of niacin

Tibia dimensions and mechanical properties were determined in White Leghorn cockerels that had been fed from 0.1 to 2.0% niacin as a supplement to standard poultry diets. Four experiments of from 20 to 38 days were conducted. No significant differences due to niacin were found in weight gain, feed consumed or feed: gain ratios. Decreases in the exterior (P < 0.009) and interior (P < 0.015) diameters of the major axes of the tibiae were found at 0.75-2.0% niacin. Exterior (P < 0.005) and interior (P < 0.001) diameters of the minor axes of the tibia were decreased at levels of 0.75 and 1%. Changes occurred in lateral wall thickness of chicks fed 0.75% niacin for 20 days (P < 0.004) and 38 days (P < 0.023) and in anterior wall thickness of 6-month-old chickens fed 1.0% niacin for 28 days (P < 0.001). Ultimate force was decreased in young chicks fed 1.0 and 1.5% niacin (P < 0.014) and 6-month-old White Leghorn chickens fed 1.0% niacin (P < 0.004). The addition of high levels of niacin to chick rations resulted in changes in dimensions, bone strength and susceptibility to fracture.