Effects of different levels of vitamins A and E on the utilization of cholecalciferol by broiler chickens.

Three experiments were conducted to determine the effects of high dietary levels of vitamins A and E on the utilization of cholecalciferol by broiler chicks. In Experiment 1, chicks were fed six levels of vitamin A (5,000, 10,000, 20,000, 40,000, 80,000, and 160,000 IU/kg). Cholecalciferol (vitamin D3) was not added to the basal diet but all birds were exposed to ultraviolet (UV) fluorescent light. Body weight was decreased only at levels of vitamin A of 80,000 IU/kg or above. In Experiment 2, birds were exposed to UV fluorescent light or no UV light, two levels of dietary vitamin A (1,500 and 45,000 IU/kg) and three levels of dietary vitamin D3 (0, 500, and 2,500 IU/kg) in a 2 x 2 x 3 factorial arrangement. The high level of vitamin A reduced (P < 0.001) bone ash but only at a marginal level of vitamin D3 (500 IU/kg) and when the birds were not exposed to UV light. In Experiment 3, birds were exposed to UV fluorescent light or no UV light, two levels of dietary vitamin E (10 and 10,000 IU/kg) and three levels of dietary vitamin D3 (0; 500 and 2,500 IU/ kg) in a 2 x 2 x 3 factorial arrangement. The high level of vitamin E significantly (P < 0.05) reduced body weight, bone ash, plasma calcium, and increased rickets but only at 500 IU/kg of vitamin D3. Feeding 2,500 IU/kg of vitamin D3 overcame the effects of the high level of vitamin E, causing a significant (P < 0.05) interaction. Ultraviolet light also prevented the detrimental effects of the high level of vitamin E. The results of these studies indicate that high dietary levels of vitamins A and E negatively affected the utilization of vitamin D3 only when D3 was present at a marginal level (500 IU/kg) in the diet but not when it was synthesized in the bird by exposure to UV light or supplemented at 2,500 IU/kg in the diet.