THE BIOAVAILABILITY OF PHOSPHORUS FROM FEED PHOSPHATES FOR BROILERS AS INFLUENCED BY BIOASSAY METHOD, DIETARY CA-LEVEL AND FEED FORM

The apparent retention of P from feed phosphates was investigated in t wo balance trials (experiments 1 and 3) using a nearly P-free basal di et and fed respectively as pellets and crumbles. Experiment 2 was a 3- factorial comparative bio-assay growth trial, involving 2688 male broi ler chicks, in which a low-P mash diet (0.7 g/kg non-phytin P) was sup plemented to P levels of 1.3, 1.9, 2.5, 3.1 and 3.7 g/kg from commerci al monobasic calcium phosphate monohydrate (MCPh) Ca(H2PO4)(2) . H2O, dihydrated dibasic calcium phosphate (DCPh) CaHPO4 . 2H(2)O and anhydr ous dibasic calcium phosphate (DCPa) CaHPO4. Asymptotic regression mod els 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 ex periment 2) on P utilization was also studied. The apparent P retentio n with the pelleted diet was on average 78.1, 74.2 and 63.6% respectiv ely for MCPh, DCPh and DCPa and significantly different (LSD = 3.3%). The effect of Ca was not significant. With the crumbled diet the appar ent P retention appeared to be distinctly higher, being 85.5 +/- 1.9 a nd 82.3 +/- 1.6 for MCPh and DCPh. The results suggest that apparent P retention is markedly influenced by diet form (hardness of the pellet s) and that the results of the latter balance trial are more useful fo r the formulation of crumbled or mash diets. The relative bio-availabi lity 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 phospha tes in the balance trials. The results from the three experiments sugg est the use of relative P utilization values in diet formulation for b roilers. (C) 1997 Elsevier Science B.V.