Cattle herd dynamics: An integer and stochastic model for evaluating production alternatives

A general cattle herd simulation model is presented in which a herd is simultaneously represented as both a biological and an economic unit. The model is time dynamic, stochastic, non-optimizing and integer, that is, it treats animals in the simulated herd as individual entities. The model provides the user with an array of policy options for weaning, breeding, milking, buying and selling stock, and supplementation to increase production or for strategic reasons during periods of drought so that herd performance can be evaluated under alternative produc tion regimes. Five general components in the model account for changes in the biological status of animals during each month of simulation : forage intake, energy require ments, production and growth, mortality and reproduction. The quantity and quality of forage on offer are specified stochastically. The parameters of math ematical relationships of the various biological processes are drawn from the literature and specified for particular systems under study based on observations from these systems. Thus, the model is data based where possible. The FORTRAN computer code is adequately modularized so alterations and refine ments can be made easily.