Originating with the global planning exercise Agriculture Toward 2000[5,6] Hallam initiated simulation experiments to evaluate and identify potential constraints on livestock numbers, herd composition, and use of feed resources in Sudan, Pakistan, and Columbia. The approach used was modular, with representations of the complete livestock industry built up as aggregations of the models of component systems. Only within the feed accounting component was the entire industry considered simultaneously. This structure had advantages in being able to manipulate any component system or combination of component systems in isolation and of facilitating analysis of changes in the livestock sector through time. These case studies serve to highlight constraints imposed by available feed resources on livestock production in developing countries.
Disease severely limits livestock production in many developing countries. Both stochastic and deterministic models of the relationship between level of disease resistance and production under constant infection pressure were developed and used to evaluate strategies to improve resistance to trypanosomosis. These models illustrate that resistance to disease will increase when selection is based only on the level of production. Further, only when heritability for resistance is low does selection on predicted production using quantitative trait loci for resistance result in greater gain for resistance and observed production than mass selection on observed production.
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