Evaluation of phytase, vitamin D3 derivatives, and broiler breed differences on nutrient utilization, broiler performance, leg disorders, and the expression of intestinal calbindin-28 kd mRNA and protein
Shirley, Robert Bryant
MetadataShow full item record
Five experiments were conducted to evaluate the effects of elevated phytase levels [0 to 12,000 units (U)/kg of diet] on broiler chick performance, tibia ash deposition, and the utilization of nutrients in total phosphorus (tP)-deficient diets. The effects of varying levels of phytase alone were evaluated in Experiment 1. Experiments 2 and 3 evaluated the interaction between varying levels phytase and dietary 25-hydroxycholecalciferol or 1a-hydroxycholecalciferol. In Experiments 4 and 5, the interactive effects of varying dietary Ca and phytase were evaluated. In each of the five phytase experiments, supplementing a tP-deficient broiler diet with 6,000 to 12,000 units of phytase hydrolyzed approximately 80 to 95% of dietary phytate. This not only reduced the P-deficiency of the broiler diets, but subsequently increased the overall Ca and P retention, performance and tibia ash deposition of broiler chicks. In Experiments 3 and 4, the addition of 25- hydroxycholecalciferol and 1a-hydroxycholecalciferol improved broiler performance and the utilization of nutrients at the lower levels of phytase supplementation, however, the addition of 1a-hydroxycholecalciferol at the higher levels of phytase depressed body weight gain and feed intake, despite graded improvements in phytate degradation and mineral retention values. This suggested that 1a-hydroxycholecalciferol improved Ca absorption to the point that it was anorexigenic. In Experiments 4 and 5, increasing the level of dietary Ca to 1.1% in a tP-deficient diet reduced broiler performance, mineral utilization, and tibia ash deposition when 0 or 1,500 U of phytase was supplemented. Increasing the level of phytase to 6,000 U/kg of diet eliminated the negative effects of high dietary Ca. These data suggest that higher levels of phytase are required to increase the liberation of phytate P. Adjustments in the ratio of dietary Ca to total P, and the level of vitamin D3 metabolites, however, should be considered when attempting to maximize broiler performance, reduce the amount of excreted P, and improve the overall quality and availability of nutrients in a tP-deficient broiler ration.