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. 2008 Jun 30;105(28):9668–9673. doi: 10.1073/pnas.0802446105

Table 3.

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

Conventional Indexed*
Conventional with rbST Organic
Milk production, kg/y × 109 101 1.00 1.00
Lactating cows × 106) 6.58 0.92 1.25
Total dairy population§ × 106) 14.0 0.92 1.25
Total land area required, ha × 106 10.3 0.95 1.30
N excretion, t/y × 103 596 0.94 1.39
P excretion, t/y × 103 303 0.95 1.34
Eutrophication potential, PO4 equivalents), kg/y × 106 452 0.95 1.28
Acidification potential** (SO2 equivalents), kg/y × 106 650 0.95 1.15
Global warming potential†† (CO2 equivalents), kg/y × 109 121 0.94 1.13

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.