In countries experiencing intense population pressure, there is seldom enough land for pasture or for crops grown specifically for livestock. In many instances they are fed the locally available agricultural by-products and scavenged mature forage, which are usually deficient in minerals, energy and protein. Animals in these situations are not primarily producers but rather serve many purposes: insurance, mobile capital, a source of fuel, traction, a fertilizer factory, and status symbols. Unsophisticated but scientifically based research has been carried out in developing countries, primarily on farms, over the past few decades seeking to optimize the production of such animals from local resources.