A dynamic model for the simulation of cattle herd production systems: Part 1—General description and the effects of simulation techniques on model results

A computerised model to describe and predict cattle production for any herd size and time period and for a wide range of environments, was developed from a model published by Sanders & Cartwright (1979a, b).The dynamics of the model are based on the flow of energy from vegetative sources to animal products in a single-animal or cow-calf unit, so that the model is appropriate even for smallholder herds. A separate flow of numbers records the dynamically changing herd size and structure.Reproduction and mortality are linked to the nutritional and physiological status of each individual. Their occurrence is triggered stochastically to preserve the integer quality of the herd. In all other respects the model is deterministic.The simulated herd can be of any number, breed, sex and age composition. Breeds are distinguished by mature size, growth rate and milk production: they can be single, dual and/or triple purpose (dairy and/or beef and/or draught). Feeding management can be grazing, stall-feeding or a combination of the two. Routines are included which can simulate different types of management decisions and their repercussions. Functions for the quantification of the model were selected according to preset guidelines, generally following an investigation of conflicting hypotheses.There are eight different output options (tabular and graphical), representing various levels of model resolution.