Cystic ovarian disease in Dutch dairy cattle, II. A simulation model for predicting the herd-level consequences under varying management factors

A state transition simulation model of cystic ovarian disease (COD) was created, in which effects of COD on calving interval and culling at the farm level can be studied. The model has 5 states: culled, fresh, cystic, pregnant and cycling. The user can define variables regarding COD and reproductive status. Output of the model consists of COD figures, calving interval and culling figures. The method of calculation and the assumptions of the model are described. With this model a simulation study was done, in which the incidence of COD, heat detection rate, interval from calving to first insemination and pregnancy rate were varied. With an increase of COD incidence with more than 10%, calving interval increased only 3 to 4 days. The influence of heat detection rate, pregnancy rate and interval calving to first insemination on the calving interval were much greater. It is therefore concluded that COD, even with a high incidence, is not a large threat to herdlevel reproductive performance.