Table 2.

Current annual resources required for a population containing one million rbST-supplemented dairy cows and parameters relating to the environmental impact of producing the same quantity of milk without rbST supplementation

ConventionalConventional with rbSTReductions with rbST use
Production parameters
    Milk production, kg/y × 10914.114.1
    Number of lactating cows*, × 1031,3381,180157
    Number of dry cows, × 10321719225
    Number of heifers, × 1031,2911,139152
Nutrient requirements
    Total maintenance energy requirement, MJ/y × 10954.147.86.3
    Total maintenance protein requirement, t/y × 10366760661
    Feedstuffs, t freshweight/y × 10625.923.72.3
Waste output
    Nitrogen excretion, t/y × 103100919.6
    Phosphorus excretion, t/y × 10345.741.44.3
    Manure, freshweight, t/y × 10634.932.22.8
Gas emissions
    Methane§, kg/y × 10649545441
    Nitrous oxide, kg/y × 103100919.6
    Carbon dioxide from livestock, kg/y × 1068,5917,812779
    Carbon dioxide from cropping, kg/y × 10655250745
    Carbon dioxide equivalents, (from CH4 and N2O), kg/y × 10912.411.41.0
    Total global warming potential, kg CO2/y × 10921.619.71.9
Cropping inputs
    Cropping land required, ha × 1032,7122,493219
    Nitrogen, kg/y × 106101928.6
    Phosphorus, kg/y × 1061211119.9
    Potassium, kg/y × 10612811711
    Herbicides, kg/y × 1031,9531,790163
    Insecticides, kg/y × 10379973267
    Fossil fuels, MJ/y × 1068,8408,111729
Resource use
    Electricity, kWh/y × 10613501195156
    Water, liter/y × 10966.961.55.4
  • One million lactating cows supplemented with rbST plus associated ineligible lactating cows, dry cows and replacement heifers.

  • *Use of rbST significantly increases milk production (7); yield response to supplementation equaled 4.5 kg per day. The conventional with rbST group includes cows receiving rbST and those in early lactation that are not eligible for rbST supplementation.

  • Refers to nutrients required for maintenance (all animals), pregnancy (dry cows) and growth (heifers).

  • Based on rations formulated to meet nutrient requirements using alfalfa hay, corn silage, corn grain and soybean meal as primary ingredients.

  • §Includes CH4 from enteric fermentation and manure fermentation.

  • Includes CO2 emissions from animals and cropping, plus CO2 equivalents from CH4 and N2O.

  • Only includes fuel used for cropping.