THE INFLUENCE OF VITAMIN-A ON THE UTILIZATION AND AMELIORATION OF TOXICITY OF CHOLECALCIFEROL, 25-HYDROXYCHOLECALCIFEROL, AND 1,25-DIHYDROXYCHOLECALCIFEROL IN YOUNG BROILER-CHICKENS

Three experiments were conducted to determine the influence of vitamin A on the utilization and amelioration of toxicity of cholecalciferol (vitamin D-3), 25-hydroxycholecalciferol [25-(OH)D-3], and 1,25-dihydr oxycholecalciferol [1,25-(OH)(2)D-3] in young broiler chicks. Two leve ls of vitamin A (1,500 and 45,000 IU/kg or 450 and 13,500 mu g) were f ed in all experiments. In Experiment 1, chicks were fed six levels of vitamin D-3 (0, 5, 10, 20, 40, and 80 mu g/kg). High dietary vitamin A decreased bone ash (P < 0.001), and increased the incidence of ricket s (P less than or equal to 0.02). Linear and quadratic responses to vi tamin D-3 levels were significant (P < 0.01) for body weight, bone ash , incidence and severity of rickets, and plasma calcium. In Experiment 2, six levels of 25-(OH)D-3 (0, 5, 10, 20, 40, and 80 mu g/kg) were a dded to the basal diet. Adding 25-(OH)D-3 increased (P < 0.001) body w eight, bone ash, and plasma calcium, and decreased rickets and plasma vitamin A. Adding 25-(OH)D-3 overcame the reduction in bone ash produc ed by high dietary vitamin A showing a significant (P less than or equ al to 0.02) interaction. In Experiment 3, six levels of 1,25-(OH)(2)D- 3 (0, 2, 4, 8, 16, and 32 mu g/kg) were added to the basal diet. High dietary vitamin A increased (P < 0.01) the incidence and severity of r ickets. Adding 1,25-(OH)(2)D-3 increased (P < 0.01) body weightl bone ash, plasma calcium, and reduced rickets and plasma and liver vitamin A. Adding 1,25-(OH)(2)D-3 overcame the reduction in bone ash, and the increase in rickets produced by high vitamin A was significant (P less than or equal to 0.05). These results indicate that high dietary vita min A (45,000 IU/kg) interferes with the utilization of vitamin D-3, 2 5-(OH)D-3 and 1,25-(OH)(2)D-3, increasing the requirement for each of them. Moreover, 45,000 IU/kg of dietary vitamin A ameliorated the pote ntial toxic effects of feeding high levels of vitamin D-3, 25-(OH)D-3 and 1,25-(OH)(2)D-3 to young broiler chickens. Further work is necessa ry to find the minimum levels of these vitamins needed to cause these effects.