<p>FEEDING AND NITROGEN LOSSES IN DAIRY HERDS</p><p>James D. Ferguson Center of Animal Health and Productivity University of Pennsylvania School of Veterinary Medicine</p><p>Leaching of nitrogen from land disposal of animal manure contributes to significant problems with eutrophication of estuaries, lakes, ponds, and streams and high nitrate concentrations in ground water in agricultural counties. Volatilization of nitrogen as ammonia from animal operations contributes to air particulate pollution and may also contribute to eutrophication of water systems on deposition into water systems. Reducing and controlling nitrogen losses to the environment from animal operations is essential to minimize their environmental impact. The efficiency of rumen capture of feed nitrogen into bacterial crude protein has a major impact on potential losses of nitrogen to the environment.</p><p>Consider a Holstein dairy cow producing 40.8 kg of milk containing 3.7% fat and 3.1% true protein consuming 631 g of nitrogen in 23.3 kg of dry matter. The flows of nitrogen in this cow would be as follows: Intake N, g 631 % of intake Milk protein, g 200 31.7 Milk NPN, g 6 1.0 Growth, g 2 .3 Fecal N, g 257 40.7 Urinary N, g 150 23.7 Scurf N, g 17 2.7 Urinary nitrogen would contain 90.3 g as urea, which would be rapidly degraded to ammonia and potentially lost as ammonia. Milk urea nitrogen would be 9 to 10 mg/dl, depending on partitioning between urine and milk. This situation represents a very efficient feeding program. These losses may vary with the proportion of corn silage and alfalfa haylage in the ration. Using fixed ration constraints to meet the energy and protein needs of this dairy cow, changing forage base may have the following consequences:</p><p>Forage % CP,% Intake N, g MilkNPN, g Fecal N, g Urine N, g CSG 100, HYLG 0 17.0 635 6.8 249 161 CSG 73, HYLG 27 18.5 691 8.8 254 210 CSG 50, HYLG 50 18.8 702 9.1 258 217 CSG 27, HYLG 73 20.1 750 11.1 257 263 CSG 0, HYLG 100 20.4 762 11.4 260 271</p><p>Forage program may have a significant impact on urinary losses at fixed production levels. In addition, the increase and decrease in forage quality can alter urinary losses. At the farm level, cattle grouping based on production and feeding appropriate rations can further reduced urinary losses. </p>