4.2.1 Herd (original) (raw)
The demand for livestock products which has been defined in Step 1 (cf. Human demand) is the starting point of the calculation (Figure 8). Next, imports are computed as the share of total consumption which is imported times the consumption for each product and time step. The exported quantity is taken from the selected scenario (cf. Trade). Consumption minus imports plus exports increased by the share of the production which is lost gives the production which is required domestically by animal product and time step. Production loss is product specific. It is computed based on FAO’s Commodity Balance (FAOSTAT, 2020) and is kept constant at 2010 levels over 2010-2050. We differentiate between dairy cattle and other cattle, dairy sheep and goats and other sheep and goats, laying hens, chicken broilers, and poultry mixed, and there is only one production system for pigs. Livestock production systems, input, output, and emission factors are taken from Herrero et al. (2013).
One difficulty in modeling the livestock sector is the fact that some animal products, such as milk, can be produced by different animals and across different production systems. In order to compute the number of animals which are required to reach the projected domestic production level, we multiply total domestic production by animal product by the contribution of each animal type and production system in the total production by animal product in 2000 as reported by Herrero et al. (2013). This parameter is constant but should be made dependent on scenarios in the future to allow for testing of structural changes in the livestock sector. Finally, the production per animal type and production system is divided by the average productivity per Tropical Livestock Unit (TLU) to compute the herd in 1,000 TLUs for each animal type, production system, and time-step. Animal productivity depends on the level in the year 2000 as reported by Herrero et al. (2013) and the productivity shifter in the selected animal productivity scenario (cf. Productivity).