A fecal test for assessing phosphorus overfeeding on dairy farms: Evaluation using extensive farm data |
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Authors: | Z. Dou C.F. Ramberg Jr. J.D. Toth L.E. Chase K.F. Knowlton |
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Affiliation: | * Section of Animal Production Systems, School of Veterinary Medicine, University of Pennsylvania, 382 West Street Road, Kennett Square 19348 † Institut de recherche pour le développement, 13572 Marseilles Cedex 02, France ‡ Department of Animal Science, Cornell University, Ithaca, NY 14853 § Department of Animal and Avian Sciences, University of Maryland, College Park 20742 # Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061 |
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Abstract: | Managing P on dairy farms requires the assessment and monitoring of P status of the animals so that potential overfeeding may be minimized. Numerous published studies have demonstrated that for lactating dairy cows, increasing P concentrations in diets led to greater P excretion in feces. More recent work reported that inorganic P (Pi) in 0.1% HCl extracts of feces (fecal extract Pi, g/kg) closely reflects dietary P changes. This has led to the proposal that 0.1% HCl fecal extract Pi may serve as an indicator of the animal's P status (adequate or excessive) when compared with a benchmark value. Here, we present the results of an extensive evaluation of the proposed fecal P indicator test. With samples (n = 575) from >90 farms, fecal total P (TP, g/kg) and fecal extract P were positively correlated with dietary P (X, g/kg): TP = 1.92X - 0.17 (R2 = 0.36); fecal extract P = 1.82X - 2.54 (R2 = 0.46). Fecal extract P was responsive to dietary P changes, whereas the remaining P, calculated as TP minus fecal extract P, was not. A provisional benchmark value of fecal extract P representing near-adequate P status was set at 4.75 g/kg. Assessment of the farm data using the benchmark indicated that 316 out of 575 data points were associated with possible P overfeeding. Advantages of the fecal-based test over feed-based analysis to assess P status are discussed. The fecal extract P method is a simple and practical test that can be used as an assessment tool for helping dairy producers improve P management and reduce their environmental footprint. |
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Keywords: | fecal P test P overfeeding dairy farm assessment |
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