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* Center for Animal Health and Productivity, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348
Dept. of Dairy Science, Cornell University, Ithaca, NY 14853
Dept. of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061
Dept. of Animal and Avian Science, University of Maryland, College Park 20742
|| Dept. of Plant and Soil Science, University of Delaware, Newark 19717
# Dept. of Dairy and Animal Science, Pennsylvania State University, State College 16802
Corresponding author: Z. Dou; e-mail: dou{at}cahp.vet.upenn.edu.
A viable and cost-effective approach to managing P on dairy farms is to minimize excess P in diets, which in turn leads to less excretion of P in manure without impairing animal performance. A questionnaire survey was conducted, coupled with on-site feed and fecal sample collection and analysis on dairy farms in New York, Pennsylvania, Delaware, Maryland, and Virginia. The purpose was to assess dietary P levels and to identify critical control points pertaining to P feeding management. Survey responses, 612 out of 2500 randomly selected farms, revealed a wide range of dietary P concentrations for lactating cows, from 3.6 to 7.0 g/kg of feed DM. The mean was 4.4 g/kg, which was 34% above the level recommended by the NRC for 27.9 kg milk/d, the mean milk yield in the survey. Higher P concentrations in diets were not associated with higher milk yields (n = 98, R2 = 0.057 for the survey farms; n = 92, R2 = 0.043 for farms selected for on-site sampling). However, higher dietary P led to higher P excretion in feces (n = 75, R2 = 0.429), with much of the increased fecal P being water soluble. Phosphorus concentrations in diet samples matched closely with P concentrations in formulated rations, with 67% of the feed samples deviating <10% from the formulations. On 84% of the survey farms, ration formulation was provided by professionals rather than producers themselves. Most producers were feeding more P than cows needed because it was recommended in the rations by these consultants. In conclusion, P fed to lactating cows averaged 34% above NRC recommendations; to reduce excess dietary P, ration formulation is the critical control point.
Key Words: dairy farm • phosphorus • diet modification
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