A model for the evaluation of different production strategies for animal production from rangeland in developing areas: An overview

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Abstract
An interactive user‐friendly computer package is being developed to assist planners and managers with the evaluation of different livestock production strategies in semi‐arid regions. It comprises a hierarchy of simulation models that predict over time the effects of past and present rainfall, stocking rates, milking and sales policies on herbage availability, body mass of cows and their progeny, output of milk for sale and herd composition. Herbage on offer is modelled daily in relation to soil moisture and defoliation. Herbage and energy consumption by each animal are functions of its size, physiological status and previous nutrition, supplementary feeding and the availability and composition of herbage. In calves the effect of milk consumption on solid food intake is also considered. Dietary energy is partitioned within the animal according to potential between body tissues, milk production and the conceptus. The inputs for the model are rainfall for every day of the period, initial body mass for each class of animal, mature cow body mass, potential secretory capacity of the udder, amount of milk for human consumption, and the initial amount of each herbage component. The user specifies sales and drought feeding policies. The model may be used to predict the effects of stocking rate, milking and milk production potential of the cow on calf growth and survival and on subsequent calving rate in years of different rainfall patterns. It shows how the timing of a management decision such as reducing the number of grazing animals or the amount of milk removed influences the subsequent performance of animals and pasture. When several years are simulated the long‐term requirements for drought feeding may be estimated.