Challenges of using tibia bone ash and toe ash as biomarkers of phosphorus nutrition for meat chickens

Challenges of using tibia bone ash and toe ash as biomarkers of phosphorus nutrition for meat chickens

Two experiments were conducted to determine the suitability of tibia bone ash and toe ash as biomarkers of phosphorus (P) status of broilers from day 1 to 21 (Experiment 1) and from day 21 to 49 (Experiment 2). Experimental diets, including sorghum, soybean meal and other minor ingredients, were formulated to meet all nutrient requirements according to the nutrition specification recommended by Aviagen Inc (2022) except for calcium (Ca) and P. The diets contained the same concentrations of Ca of 10.0 and 9.0 g/kg diet for starter and grower/finisher, respectively and graded levels of non-phytate P (NPP) from 2.5 to 5.5 g/kg diet for starter; from 2.0 to 5.0 g/kg diet for grower/finisher in increment of 1.0 g/kg. Each diet was fed to one of five replicate pens (10 chicks per pen), starter from day 1 to 14; grower from day 15 to 28 and finisher from day 29 to 49. Body weight and feed intake were recorded weekly and feed conversion ratios (FCR) calculated. Ash content of tibia bones and toes were determined at the completion of both experiments. The results indicated that the NPP requirement of meat chickens was lower than the NRC (1994) recommendations and values currently used by the industry. Phytase supplementation significantly (P < 0.05) increased body weight of birds fed diets containing the lowest NPP concentrations (2.5/2.0 and 3.5/3.0 g/kg), but had no effect when the NPP levels were 4.5/4.0 and 5.5/5.0 g/kg. Growth performance and FCR are recommended as the primary parameters for evaluating the P requirement of meat chickens. Tibia bone and toe ash contents were poorly correlated with growth performance and were therefore not good biomarkers of dietary P status, especially in finisher birds. Only one Ca concentration was used in the current study and further research on P nutrition with different concentrations of Ca with or without supplemental phytase is warranted.