Harmful effects of nicotinic acid occur at levels far in excess of requirements. Limited research indicated that nicotinic acid and nicotinamide are toxic at dietary intakes greater than about 350 mg per kg (160 mg per lb) of body weight per day (NRC, 1987). Clinical signs for niacin toxicosis in chicks include reduced egg production, growth retardation, short legs and coarse, dense feathering. High dietary levels of niacin (0.75% to 2.0%) fed to broilers were detrimental to dimensions and mechanical properties of bone (Johnson et al., 1992; 1995). There was no change in the mineral content of the tibia, but bone strength decreased with increased susceptibility to fracture.
