Effects of the composition of the basal diet on the evaluation of mineral phosphorus sources and interactions with phytate hydrolysis in broilers

Abstract

The objectives of this study were to determine the availability of P from mineral phosphate sources by using different basal diets and measurement of P retention and prececal (pc) P digestibility as well as pc myo-inositol phosphate (InsP) degradation in broilers. Semi-synthetic and corn-soybean meal-based basal diets were used in experiment 1, and corn-based and wheat-based basal diets were used in experiment 2. Anhydrous monosodium phosphate (MSPa) or monocalcium phosphate monohydrate (MCPh) was supplemented to increment the P concentration by 0.05, 0.10, and 0.15% or by 0.075 and 0.150% in experiments 1 and 2, respectively. Titanium dioxide was used as an indigestible marker. Diets were pelleted through a 3-mm screen. In experiment 1, retention was measured based on total excreta collection from 20 to 24 d of age using 7 replicated birds per diet. In experiment 2, digesta from the terminal ileum was collected from 22-d-old broilers penned in groups of 19 with 5 replicated pens per diet. The P retention response to supplemented MSPa did not differ between the 2 basal diets in experiment 1. The response in pc P digestibility to MCPh supplements also did not differ between the 2 basal diets in experiment 2, as calculated by linear regression analysis. Hydrolysis of InsP6 measured on both the excreta and pc levels was high in the basal diets without a mineral P supplement. Mineral P supplementation significantly decreased (P < 0.05) InsP6 hydrolysis from the InsP-containing diets in both experiments. Thus, the choice of the basal diet did not affect the evaluation of the supplemented mineral P source. However, calculated values for mineral P sources need to be adjusted for the decline in hydrolysis of InsP contained in the basal diet that results from the P supplement.