ABSTRACT
Variable quantities of vitamin D3 (D3) ranging from 0 to 20,000 IU D3/kg of diet were incorporated in a corn-soybean meal basal diet and fed to male broiler chicks from day-old until 56 days of age. Four experiments were conducted to determine: 1) the requirement of D3 for growth and bone calcification of normal chicks, 2) the requirement of D3 for deficient chicks, and 3) if feeding up to 20,000 IU D3/kg of diet affects bone metabolism or increases the incidence of leg abnormalities. The parameters measured included: body weight, feed consumption, feed conversion, mortality rate, ionic and total serum calcium, kidney calcium, total blood phosphorus, tibial ash, tibial breaking strength, and tibial length. In addition, the type and the incidence of occurrence of skeletal abnormalities were recorded. The data indicate that feeding less than 200 IU D3/kg of diet produced significantly lower body weights, feed consumption and conversion values, serum ionic calcium, total serum calcium, tibial breaking strength, and percentage tibial ash values (P less than .05). For example, rachitic chicks fed 200 IU D3/kg of diet had significantly lower (P less than .05) levels of ionic calcium at 21 days than rachitic chicks fed 300, 400, or 1,500 IU D3/kg of diet. The optimal level of D3 for 0 to 56-day-old male broiler chicks, based on body weight and percentage tibial ash, is 400 IU D3/kg of diet. The vitamin D3 requirement for deficient chicks repleted with D3 appears to be between 300 to 400 IU D3/kg of diet. Feeding 1,500 to 20,000 IU D3/kg of diet does not appear to alter bone metabolism or increase the incidence of leg abnormalities.