Livestock systems/Data uncertainties limitations
Parts of Livestock systems
|Component is implemented in:|
|Related IMAGE components|
Data, uncertainties and limitations
Livestock numbers, milk production per animal, off-take rates and carcass weights for the 1970–2005 period were obtained from FAO (FAO, 2012a). Various animal production systems, and the total livestock population and production have been defined in recent FAO publications (Seré and Steinfeld, 1996). For ruminants, these production systems include pastoral, mixed and landless production in various agro-ecological zones. These data have been aggregated to two systems: pastoral, and mixed & landless production systems, and disaggregated from seven world regions to the 24 world regions in the IMAGE model (Bouwman et al., 2005). Seré and Steinfeld, 1996 also provided data on the growth in livestock populations and on production in each production system.
There are several uncertainties in the calculation of livestock production in the different systems for historical years and scenarios. The first uncertainty is the aggregation level on the scale of country or world region, which does not take account of underlying heterogeneity. The second uncertainty concerns the use of average data for carcass weight, off-take rate, and milk production for total livestock populations. In reality, livestock populations cover different age classes, and not all animals in a population are productive. Calculations, such as energy requirement for maintenance, are a non-linear function of body weight, and thus use of average values, may lead to distortion. The third uncertainty is associated with livestock numbers. Methodology and frequency of data collection (for example, by census) vary between countries, and are probably less certain for some developing countries than for industrialised countries. This uncertainty on livestock numbers affects not only the livestock module, but also all impact IMAGE modules that depend on livestock numbers, such as ammonia emissions (Beusen et al., 2008).
The main uncertainties in construction scenarios concern agricultural demand (Agricultural economy), the distribution of production over the two systems, and production characteristics per system, including feed requirements and feed types.
The key limitation in the current livestock module is that the ruminant livestock system have a soft linkage to the agricultural economy model MAGNET (Agricultural economy). Although MAGNET has some representation of feed substitution and intensification as a result of land scarcity, and mimics the dynamics described here, there is no explicit representation of livestock systems, and physically based feed compositions.