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a USDA-ARS, Northwest Irrigation and Soils Research Lab., 3793 N. 3600 E., Kimberly, ID 83341-5076, USA
b Dep. of Poultry Science, College of Agriculture and Life Sciences, Campus Box 7608, North Carolina State Univ., Raleigh, NC 27695-7608
c Crop and Soil Environmental Sciences Dep. (0404), Virginia Tech, Blacksburg, VA 24061
d USDA-ARS, Soybean and Nitrogen Fixation Research Unit, 3127 Ligon St., Raleigh, NC 27607
* Corresponding author (leytem{at}nwisrl.ars.usda.gov)
Received for publication August 22, 2006. Environmental concerns about phosphorus (P) losses from animal agriculture have led to interest in dietary strategies to reduce the concentration and solubility of P in manures and litters. To address the effects of dietary available phosphorus (AvP), calcium (Ca), and phytase on P excretion in broilers, 18 dietary treatments were applied in a randomized complete block design to each of four replicate pens of 28 broilers from 18 to 42 d of age. Treatments consisted of three levels of AvP (3.5, 3.0, and 2.5 g kg–1) combined with three levels of Ca (8.0, 6.9, and 5.7 g kg–1) and two levels of phytase (0 and 600 phytase units [FTU]). Phytase was added at the expense of 1.0 g kg–1 P from dicalcium phosphate. Fresh litter was collected from pens when the broilers were 41 d of age and analyzed for total P, soluble P, and phytate P as well as P composition by 31P nuclear magnetic resonance (NMR) spectroscopy. Results indicated that the inclusion of phytase at the expense of inorganic P or reductions in AvP decreased litter total P by 28 to 43%. Litter water-soluble P (WSP) decreased by up to 73% with an increasing dietary Ca/AvP ratio, irrespective of phytase addition. The ratio of WSP/total P in litter decreased as the dietary Ca/AvP ratio increased and was greater in the phytase-amended diets. This study indicated that while feeding reduced AvP diets with phytase decreased litter total P, the ratio of Ca/AvP in the diet was primarily responsible for effects on WSP. This is important from an environmental perspective as the amount of WSP in litter could be related to potential for off-site P losses following land application of litter.
Abbreviations: AvP, dietary available P • FTU, phytase activity is expressed as "phytase units" or "FTU" per unit of feed (One phytase unit is the amount of phytase that liberates 1 micromole of inorganic phosphorus per minute from an excess of sodium phytate at pH 5.5 and 37 degrees Celsius) • HPLC, high performance liquid chromatography • IP, inorganic phosphorus • NMR, nuclear magnetic resonance spectroscopy • NPP, non-phytate phosphorus • PSC, phosphorus source coefficient • DRP, dissolved reactive P • SRP, soluble reactive P • WSP, water-soluble P
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