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
| Conventional | Conventional with rbST | Reductions with rbST use | |
|---|---|---|---|
| Production parameters | |||
| Milk production, kg/y × 109 | 14.1 | 14.1 | |
| Number of lactating cows*, × 103 | 1,338 | 1,180 | 157 |
| Number of dry cows, × 103 | 217 | 192 | 25 |
| Number of heifers, × 103 | 1,291 | 1,139 | 152 |
| Nutrient requirements | |||
| Total maintenance energy requirement†, MJ/y × 109 | 54.1 | 47.8 | 6.3 |
| Total maintenance protein requirement†, t/y × 103 | 667 | 606 | 61 |
| Feedstuffs‡, t freshweight/y × 106 | 25.9 | 23.7 | 2.3 |
| Waste output | |||
| Nitrogen excretion, t/y × 103 | 100 | 91 | 9.6 |
| Phosphorus excretion, t/y × 103 | 45.7 | 41.4 | 4.3 |
| Manure, freshweight, t/y × 106 | 34.9 | 32.2 | 2.8 |
| Gas emissions | |||
| Methane§, kg/y × 106 | 495 | 454 | 41 |
| Nitrous oxide, kg/y × 103 | 100 | 91 | 9.6 |
| Carbon dioxide from livestock, kg/y × 106 | 8,591 | 7,812 | 779 |
| Carbon dioxide from cropping, kg/y × 106 | 552 | 507 | 45 |
| Carbon dioxide equivalents, (from CH4 and N2O), kg/y × 109 | 12.4 | 11.4 | 1.0 |
| Total global warming potential¶, kg CO2/y × 109 | 21.6 | 19.7 | 1.9 |
| Cropping inputs | |||
| Cropping land required, ha × 103 | 2,712 | 2,493 | 219 |
| Nitrogen, kg/y × 106 | 101 | 92 | 8.6 |
| Phosphorus, kg/y × 106 | 121 | 111 | 9.9 |
| Potassium, kg/y × 106 | 128 | 117 | 11 |
| Herbicides, kg/y × 103 | 1,953 | 1,790 | 163 |
| Insecticides, kg/y × 103 | 799 | 732 | 67 |
| Fossil fuels‖, MJ/y × 106 | 8,840 | 8,111 | 729 |
| Resource use | |||
| Electricity, kWh/y × 106 | 1350 | 1195 | 156 |
| Water, liter/y × 109 | 66.9 | 61.5 | 5.4 |
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.