Voluntary food intake and diet selection, along with the food intake capacity of the animal, are important subjects as they control the amount of nutrients consumed by an animal relative to its requirements for maintenance and level of production. The basic and complex concepts underlying their regulation and integration are pointed out and briefly discussed. In desert animals, including sheep, these subjects are more complex and even more important because of the super-imposed direct and indirect effects of the environment, including food availability in quantity and quality. The practices undertaken by shepherds attempting to correct seasonal deficiencies on the one hand, and the animals' adaptive capacities on the other hand, among other factors, have or can exert modifying effects. Examples include concentrate supplementary feeding, the use of cultivated shrubs as forage reserve and water deprivation and salinity. In this context, long-term adaptation is of paramount importance. Sample experimental data are presented and discussed.