Phosphorus Feeding Levels and Critical Control Points on Dairy Farms

Abstract 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 7.0g/kg of feed DM. The mean was 4.4g/kg, which was 34% above the level recommended by the NRC for 27.9kg milk/d, the mean milk yield in the survey. Higher P concentrations in diets were not associated with higher milk yields (n=98, R 2 =0.057 for the survey farms; n=92, R 2 =0.043 for farms selected for on-site sampling). However, higher dietary P led to higher P excretion in feces (n=75, R 2 =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