Phosphorus Characteristics of Dairy Feces Affected by Diets
- Zhengxia Dou *a,
- Katharine F. Knowltonb,
- Richard A. Kohnc,
- Zhiguo Wude,
- Larry D. Satterd,
- Gangya Zhange,
- John D. Totha and
- James D. Fergusona
- a Center for Animal Health and Productivity, School of Veterinary Medicine, Univ. of Pennsylvania, 382 West Street Road, Kennett Square, PA 19348
b Dep. of Dairy Sci., Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
c Dep. of Animal and Avian Sciences, Univ. of Maryland, College Park, MD 20742
d U.S. Dairy Forage Research Center, Madison, WI 53706
e Soil Science Institute, Chinese Academy of Sciences, Nanjing, China
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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