Livestock production is an important food supply and economic activity, the primary goal of which is to supply high-quality protein (meat, eggs, dairy products, etc) for the needs of human populations. The animals serve as concentrated sources of typically dispersed nutrients. Subsidiary products may include leather, fertilizers, inputs to animal feeds, and energy sources (biofuels). The challenge of sustainable livestock production systems is to promote food security in a manner which is economically viable and socially acceptable without causing land degradation or irreversibly affecting ecological resilience. As such, sustainability must promote a favourable cost – benefit ratio, and as far as possible avoid reducing the set of options available to future generations. This has very significant social considerations, as seemingly obvious solutions may be difficult to implement, as they may be biologically but not economically sustainable.

The recycling of materials, and thus minimizing the generation of wastes is a basic process which must be implemented to meet the demands of sustainability in developed and developing countries alike. Systems which utilize energy produced from biomass are examples of energy-recycling systems. All biomass originates through carbon dioxide fixation by photosynthesis. Consequently, biomass utilization may be regarded as a critical component of the global carbon cycle of the biosphere...

http://geoenergy.wordpress.com/2008/08/12/biomass-energy-%e2%80%93-sustainable-solution-to-livestock-wastes/