Wednesday, November 15, 2006 - 9:15 AM

What Controls Water Soluble Phosphorus in Broiler Litter: Available Phosphorus, Phytase, or Calcium?.

April Leytem1, Peter Plumstead2, Rory Maguire3, Prachuab Kwanyuen1, and John Brake2. (1) USDA-ARS, 3793 N 3600 E, Kimberly, ID 83341-5076, (2) North Carolina State Univ, Dept of Poultry Science, Scott Hall 261, Box 7608, Raleigh, NC 27695, (3) Univ of Virginia, Crop and Environmental Sciences Dept, 211 Latham, Blacksburg, VA 24061

Soluble phosphorus (P) in litter and manure is important from an environmental perspective as it is related to potential off site P losses following land application. The effects of amending dietary P, calcium (Ca), and phytase on manure and litter P excretion in broilers were investigated. A 3 x 3 x 2 factorial treatment structure was applied from 14 to 42 d of age with three levels of available P (AvP) (0.35%, 0.30%, and 0.25%) combined with three levels of Ca (0.80%, 0.69%, and 0.57%) with two levels of phytase (0 and 600 FTU) applied. The AvP level of phytase-amended diets was held constant by replacing 0.10% of the inorganic P from dicalcium phosphate with 600 FTU of phytase, while Ca and AvP levels of diets were varied by altering proportions of limestone, dicalcium phosphate, and an inert filler. To assess treatment effects on P excretion, fresh litter was collected when the broilers were 41 d of age. Litter was analyzed for total and soluble P. Results indicated that the inclusion of phytase at the expense of inorganic P, or reductions in AvP decreased total P excretion. Soluble P in the litter decreased with dietary AvP at a constant Ca level. The ratio of Ca:AvP in the diets was negatively correlated with the solubility of P in the litter. The ratio of litter soluble P:total P increased with phytase additions at all ratios of Ca:AvP. This study indicates 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 soluble P.