CHANGES IN DIMENSIONS AND MECHANICAL-PROPERTIES OF BONE IN CHICKS FEDHIGH-LEVELS OF NIACIN

Tibia dimensions and mechanical properties were determined in White Le ghorn cockerels that had been fed from 0.1 to 2.0% niacin as a supplem ent 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 exte rior (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) aci d interior (P < 0.001) diameters of the minor axes of the tibia were d ecreased at levels of 0.75 and 1%. Changes occurred in lateral wall th ickness 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 fe d 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 Whit e Leghorn chickens fed 1.0% niacin (P < 0.004). The addition of high l evels of niacin to chick rations resulted in changes in dimensions, bo ne strength and susceptibility to fracture.