The bio-availability of phosphorus from feed phosphates for broilers as influenced by bio-assay method, dietary Ca-level and feed form

The apparent retention of P from feed phosphates was investigated in two balance trials (experiments 1 and 3) using a nearly P-free basal diet and fed respectively as pellets and crumbles. Experiment 2 was a 3-factorial comparative bio-assay growth trial, involving 2688 male broiler chicks, in which a low-P mash diet (0.7 g/kg non-phytin P) was supplemented to P levels of 1.3, 1.9, 2.5, 3.1 and 3.7 g/kg from commercial monobasic calcium phosphate monohydrate (MCPh) Ca(H2PO4)2 · H2O, dihydrated dibasic calcium phosphate (DCPh) CaHP04 · 2H2O and anhydrous dibasic calcium phosphate (DCPa) CaHP04. Asymptotic regression models were fitted to the response parameter toe ash-% to derive relative P bio-availability values for the feed phosphates. The effect of two Ca levels (9.1 vs. 10.5 g/kg in experiment 1 and 8.5 vs. 10 g/kg in experiment 2) on P utilization was also studied. The apparent P retention with the pelleted diet was on average 78.1, 74.2 and 63.6% respectively for MCPh, DCPh and DCPa and significantly different (LSD = 3.3%). The effect of Ca was not significant. With the crumbled diet the apparent P retention appeared to be distinctly higher, being 85.5 ± 1.9 and 82.3 ± 1.6 for MCPh and DCPh. The results suggest that apparent P retention is markedly influenced by diet form (hardness of the pellets) and that the results of the latter balance trial are more useful for the formulation of crumbled or mash diets. The relative bio-availability of P from MCPh, DCPh and DCPa, obtained in the comparative trial was respectively 100, 93 and 85. This ranking was comparable with the relative ranking based on the apparent P retention in the feed phosphates in the balance trials. The results from the three experiments suggest the use of relative P utilization values in diet formulation for broilers.