Experimental approach to optimize phytate phosphorus utilization by broiler chickens by addition of supplements

Supplementation of 1alpha-hydroxycholecal-ciferol (1alpha-OHD(3)), phytase, and Ca levels has been shown to influence phytate P utilization. Two experiments were conducted with 1- to 16-d broilers to investigate the interactions between the effects of 1alpha-OHD(3), phytase, and Ca on phytate P utilization. In experiment 1, the birds were randomly allocated to 13 treatments with 6 levels of 1alpha-OHD(3) from 0 to 11microg/kg, with and without 500 U/kg of phytase supplemented to P-deficient diet. A positive control diet, adequate in Ca and P, was included. In experiment 2, a 3-dimensional rotatable design with 5 levels each of 1alpha-OHD(3), phytase, and Ca was implemented. Supplementation of 1alpha-OHD(3) and phytase increased phytate P utilization, as indicated by an increase in bone ash, phytate P disappearance, and BW. In experiment 1, no interaction between the 1alpha-OHD(3) and phytase effects was determined for any criteria, except for the incidence of P rickets. However, the second experiment showed that there were interactions between the 3 factors (1alpha-OHD(3), phytase, and Ca). The probabilities that observed variation in the 3-way interaction for measured criteria that were due to chance are: BW gain = 0.1364, G:F = 0.11, bone ash percentage = 0.0278, milligrams of bone ash/tibia = 0.0909, Ca rickets = 0.9394, P rickets = 0.4892, tibial dyschondroplasia = 0.5927, and phytate P disappearance = 0.1126. The equations obtained from the regression models were used to generate contour-surface plots. The percentage of bone ash data indicated that low Ca, high phytase, and high 1alpha-OHD(3) levels were needed to optimize phytate P utilization. The results of this study show that this experimental design may be utilized to identify the best levels of nutrients to add to a diet where complex 3-way interactions exist affecting several criteria. The equations may be used to optimize performance based on desired levels of performance and the costs of the inputs.