Table 3.

Projected environmental impact of different dairy management systems on the production of sufficient milk to meet USDHHS/USDA dietary guidelines

ConventionalIndexed*
Conventional with rbSTOrganic
Milk production, kg/y × 1091011.001.00
Lactating cows × 106)6.580.921.25
Total dairy population§ × 106)14.00.921.25
Total land area required, ha × 10610.30.951.30
N excretion, t/y × 1035960.941.39
P excretion, t/y × 1033030.951.34
Eutrophication potential, PO4 equivalents), kg/y × 1064520.951.28
Acidification potential** (SO2 equivalents), kg/y × 1066500.951.15
Global warming potential†† (CO2 equivalents), kg/y × 1091210.941.13
  • Total milk requirement calculated according to USDHHS/USDA (3) recommendations for adult dairy product intakes and U.S. Census Bureau (66) population estimate for 2040.

  • *Conventional values set to equal 1.0, and values for conventional with rbST or organic production systems are expressed according to this index.

  • The conventional with rbST group includes rbST-supplemented lactating cows and cows in early lactation not yet eligible for rbST-supplementation (<57 days in milk). The conventional and organic groups include all lactating cows.

  • §Includes lactating cows, dry cows and replacement heifers.

  • Includes land area required for crop production (all groups) plus pasture (organic group only).

  • PO4 equivalents based on PO4 =1.00, N2O = 0.44 and NH4 = 0.43.

  • **SO2 equivalents based on N2O = 0.7 and NH4 = 1.88.

  • ††CO2 equivalents based on CO2 = 1, CH4 = 25 and N2O = 298.