STRUCTURE AND BEHAVIOR OF A DETERMINISTIC MODEL OF REPRODUCTIVE-PERFORMANCE IN BEEF-CATTLE

The structure and behavior of a deterministic model of reproductive performance in beef cattle is presented. The model is written in PASCAL and runs rapidly on a microcomputer using a one day timestep and producing yearly output. Annual calving percentage is calculated based on three biological variables (gestation length, length of postpartum anestrus and conception rate) and one managerial variable (breeding season length). Convergence to a steady state calving percentage was observed for a wide variety of initial parameter values, indicating a convergence of distribution from an initial uniform distribution. Steady state values display nonlinear responses to changes in the driving variables, typical of beef production operations in North America. The model was challenged by testing predicted values of annual calving percent against values observed in 136 single-sire herds over eight years as breeding season length changed. Results of the challenge indicate that the model adequately predicts reproductive performance, but changing only breeding season length resulted in consistent overprediction of annual calving percent. Accurate prediction requires accurate measurement of all four driving variables. © 1990.