title: Phosphorus characteristics of dairy feces affected by diets.
abstract: Phosphorus (P) surplus on dairy farms, especially confined operations, contributes to P buildup in soils with increased potential for P loss to waters. One approach to reduce P surplus and improve water quality is to optimize P feeding and improve P balance on farms. Here we report how varying P concentrations in lactating cow diets affects the amount as well as the chemical forms and fraction distribution of P in fecal excretion, and the environmental implications of this effect. Analysis of fecal samples collected from three independent feeding trials indicates that increasing dietary P levels through the use of P minerals not only led to a higher concentration of acid digest total phosphorus (TP) in feces, but more importantly increased the amount and proportion of P that is water soluble and thus most susceptible to loss in the environment. For instance, with diets containing 3.4, 5.1, or 6.7 g P kg(-1) feed dry matter (DM), the water-soluble fraction of fecal P was 2.91, 7.13, and 10.46 g kg(-1) fecal DM, respectively, accounting for 56, 77, and 83% of acid digest TP. The other fecal P fractions (those soluble in dilute alkaline and acid extractants) remained small and were unaffected by dietary P concentration. Excess P in the P supplemented diets was excreted in feces as water-soluble forms. A simple measure of inorganic phosphorus (Pi) in a single water extract is highly responsive to changes in diet P concentrations and hence can be indicative of dietary P status. A fecal P indicator concept is proposed and discussed.
authors.affiliation: Center for Animal Health and Productivity, School of Veterinary Medicine, Univ. of Pennsylvania, 382 West Street Road, Kennett Square, PA 19348, USA. dou@cahp.vet.upenn.edu
authors.forename: Zhengxia
authors.initials: Z
authors.lastname: Dou
authors.forename: Katharine F
authors.initials: KF
authors.lastname: Knowlton
authors.forename: Richard A
authors.initials: RA
authors.lastname: Kohn
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wu
authors.forename: Larry D
authors.initials: LD
authors.lastname: Satter
authors.forename: Gangya
authors.initials: G
authors.lastname: Zhang
authors.forename: John D
authors.initials: JD
authors.lastname: Toth
authors.forename: James D
authors.initials: JD
authors.lastname: Ferguson
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle; D004032:Diet; D005243:Feces / Q000737:chemistry*; D005260:Female; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus