Phosphorus characteristics of dairy feces affected by diets.
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.
Dou
Zhengxia
Z
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
Knowlton
Katharine F
KF
Kohn
Richard A
RA
Wu
Zhiguo
Z
Satter
Larry D
LD
Zhang
Gangya
G
Toth
John D
JD
Ferguson
James D
JD
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*
D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus