A model simulating the production of dual purpose replacement heifers

A dynamic model simulating the production of replacement in a dual purpose herd for evaluation of alternative production strategies is presented. The model simulates the herd behaviour by state transitions of individual heifers, a flow of heifers and cows through the system and a seasonal cycle. The description of the individual heifer includes a specification of actual location which, due to constraints on management and a queue sytem, plays an important role in the model behaviour. Discrete events and individual variation between heifers are triggered stochastically. The model is controlled by a set of decision variables specifying the production system and a production strategy concerning feeding, grazing, reproduction, and culling. Model behaviour is exemplified by results showing that seasonal variation due to grazing management can have a surprising effect on the production of replacement heifers.