Measurement of Endogenous Phosphorus Losses in Broiler Chickens

The experiment reported herein was conducted to estimate the ilea! and excreta endogenous phosphorus (P) losses in broiler chickens. Three purified diets, namely a P-free diet, a gelatin-based diet containing negligible amounts of P, and a casein-based diet with 100% available P, were formulated. Test diets were offered ad libitum from day 25 to 28 post hatch and ileal digesta were collected. Excreta samples were also collected to estimate total tract endogenous P losses. Ileal endogenous P losses in birds fed the casein-based diet were higher (P<0.05) than those in birds fed P-free and gelatin-based diets. The ilea! endogenous losses of P in birds fed P-free, gelatin-based, and casein-based diets were 25, 104 and 438 mg/kg dry matter intake, respectively. The endogenous P loss values estimated at the excreta level were 830, 560 and 372 mg/kg dry matter intake, respectively. Ileal and excreta endogenous losses of P in birds fed a casein-based diet were similar (P>0.05), but ileal losses were lower (P<0.05) than the excreta values in birds fed P-free and gelatin-based diets, resulting in a significant (P<0.001) assay diet by site of measurement interaction. The present data demonstrate that values determined for endogenous P losses in broiler chickens vary widely depending on the assay diet used.