Simulated livestock dynamics--effects of pastoral offtake practices and drift on cattle wealth.

Pastoral cattle herds were simulated to demonstrate a species-independent package (DADAS) for the analysis and simulation of livestock dynamics. A cow culling age of 11 years was expected to maximise offtake rate and to stabilise the cattle population. This threshold was derived by the deterministic module of the package used. A closer look at six offtake patterns using the stochastic module of the simulation program revealed that those who cull cows at an age limit would fare less well than those who cull cows only when sterile. Within each offtake pattern the cumulative effects of chance fluctuations in sex-ratio of calves, mortality, sterility, age at first calving and calving interval resulted in cattle wealth indicators varying widely between replicate herds. The example shows that livestock dynamics simulation on personal computers is feasible for planning, teaching and research purposes.