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.