Worksheet(s) in the FABLE Calculator:
⇒ 2_calc_livestock
⇒ 2_data_livestock
The computation of the production from the livestock sector is the second step in the FABLE Calculator. The livestock sector supplies animal food products (cf. Appendix 1) and consumes other agricultural products for animal feed. This explains why we need to compute the production of the livestock sector before the production of the crop sector. The objective of this calculation step is to compute the evolution of the livestock herd which then determines the feed demand and the pasture area which are used in the calculation steps that follow.
The demand for livestock products which has been defined in Step 1 (cf. Human demand) is the starting point of the calculation (Figure 4). Next, imports are computed as the share of total consumption which is imported times the consumption for each product and time step. 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, 2019) 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 modelling 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 1000 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).
The herd number by animal type and production system which is computed during the previous computing step is the starting point for the calculation of feed demand (cf. Herd). We use the feed requirements per TLU computed by Herrero et al. (2013) for corn, wheat, sorghum, rice, barley, other cereals, and soybean, for each animal type and production system. The current assumption is that these feed requirements are proportionally adjusted with changes in animal productivity (cf. Productivity). In reality, several factors could explain a lower increase in animal feed than in animal productivity so this assumption might lead to overestimation of the increase in animal feed demand over time when productivity gains are high.
The total herd number for ruminants (cattle, sheep and goats) is the starting point for the calculation of the pasture area (cf. Herd). We then divide the number of ruminants by the average ruminant density per hectare to obtain the targeted pasture area. By default, historical ruminant density is computed using the FAOSTAT ruminant numbers divided by the grassland area for 2000, 2005, and 2010 and kept constant at 2010 levels over 2015-2050. However, an optional update package for implementing alternative scenarios about the evolution of the ruminant density is available (cf. Ruminant density).
