A set of simulations were run to estimate the impact on gross margins due to improvements in cattle breeding efficiency and other management factors in extensive pastoral systems in Western Australia. The output from the simulations was integrated into a statistical model of gross margin as a function of breeding and management variables. The simulations showed that gross margin was an increasing function of breeding rates, but age at first breeding and age at sale of offspring had variable effects on the gross margin of the enterprise. The statistical model illustrated that for a one per cent increase in breeding rates, an increase in gross income of $5274 was possible. The optimal ages at first breeding and sale of offspring were 20.6 months and 10.8 months respectively. Information generated by the simulation and the statistical model allows management to identify the breakeven value, or limit of expenditure, of changes to the system, beyond which the change will not increase enterprise gross margin.