Comparative study on the effect of variable phosphorus intake at two different calcium levels on P excretion and P flow at the terminal ileum of laying hens.

Abstract

A 3 x 2-factorial balance trial was conducted with dietary concentrations of P below the requirement (3.6, 4.3 and 5.0 g/kg DM) and Ca below or at the requirement (28 and 37 g/kg DM) adjusted by monobasic calcium phosphate (MCP, Ca(H2PO4)2) and calcium carbonate (CaCO3). The diets were mainly based on maize and soybean meal. Six 18-week old laying hens were allocated to each of the diets, and excreta were quantitatively collected for 21 days from week 22 of age onwards. Feed allowance was 95 g/d according to pre-treatment ad libitum intake of the hens receiving the lowest P concentration. After the balance trial was terminated, ileal digesta was obtained from each hen, and the flow at the terminal ileum was calculated using TiO2 as indigestible marker. Linear regression analysis was applied to determine the effect of supplementary P. Hens were in a negative energy balance, indicated by a loss in BW across all treatments. Intake and excretion of both N and energy were not significantly affected by the P or Ca content of the diet. P from supplemented MCP was almost completely recovered in excreta, irrespective of dietary Ca concentration. At the terminal ileum, however, the P flow was not significantly affected by the MCP supplementation. Net absorption of P from MCP was almost complete until the terminal ileum, but P was re-directed into the excreta, likewise via the urine. The supplementation of Ca reduced praecaecal net absorption and utilisation of P from the basal diet, likewise due to a reduced phytate hydrolysis. It is suggested by the data, that comparative measurements of P availability for laying hens should be conducted on the basis of praecaecal net absorption rather than on total excretion measurements.