Parts of Livestock systems
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Model description of Livestock systems
IMAGE distinguishes two livestock production systems, namely pastoral systems, and mixed and industrial systems, based on FAO (Seré and Steinfeld, 1996). Pastoral systems are mostly dominated by extensive ruminant production, while mixed and industrial systems are more intensive with animal husbandry comprising grazing ruminants and monogastrics. The distribution of livestock production in the two systems is constructed from historical data for the years up to the present, and for future years will depend on the scenario selected.
IMAGE distinguishes five types of livestock: beef, dairy cattle (large ruminants), the category sheep & goats (small ruminants), pigs, and poultry (monogastrics). The numbers of animals and the proportion per production system are calculated from data on domestic livestock production per region provided by the agro-economic model MAGNET (Agricultural economy). The number of animals in each of the five livestock types is calculated from the total production per region and the characteristics of the livestock systems in that region. Stocks of dairy cows (POP) per country and world region are obtained from total milk production (PROD) and milk production per animal (MPH)
Animal stocks per region of beef cattle, pigs, and sheep and goats are obtained from production and carcass weight (CW) and off-take rate (OR):
Historical data on milk production per cow, off-take rate, and carcass weight are obtained from statistics, and values for future years will depend on the scenario selected.
For dairy cattle, the energy requirements are calculated for maintenance (based on body weight), feeding (based on the proportion of grass in feed rations), lactation (based on milk production per cow) and pregnancy (based on the number of calves per year). The amount of feed dry matter is calculated on the basis of the proportion of digestible energy in the total energy intake, and the energy content of biomass.
Energy requirements for cattle are based on animal activity and production, and for pigs, poultry, sheep and goats on Feed Conversion Ratios (FCR). This is the amount of feed (kg dry matter) required to produce one kilogram of milk or meat. The FCR values are based on historical data and values for future years will depend on the scenario selected.
Cropland and grassland required
Areas for feed crop production and grass are calculated on the basis of feed crop and grass requirements (Land-use allocation), which are calculated from total feed requirement and diet composition (feed rations, see below). Composition of animal feed IMAGE distinguishes five feed categories:
- grass, including hay and grass silage;
- food crops and processing by-products;
- crop residues in the field after harvesting, and fodder crops;
- animal products;
- foraging including roadside grazing, scavenging household waste, and feedstuffs from backyard farming.
In pastoral ruminant production systems, the feed is almost entirely grass except in developing regions where foraging constitutes a larger but variable proportion of the total feed. Pigs and poultry are fed feed crops and by-products, crop residues and fodder. Since these animals are mainly farmed in mixed systems, the contribution of feed crops and residues to the total feed in these systems is much higher than in pastoral systems.
The required feed crop production per animal is calculated from feed rations, and this information is incorporated into the agro-economic model (Agricultural economy). The proportion of grass in feed rations determines total grass consumption, which is used to compute the grassland area per world region, based on grazing intensity (Agricultural economy and Land-use allocation).
A scenario includes assumptions on milk production per animal for dairy cattle, carcass weight and off-take rate for beef cattle, pigs, poultry, sheep and goats, and feed conversion rates (FCR) for pigs, poultry, sheep and goats. The changes in these parameters are generally based on the scenario, and on the economic growth scenario.