[Productive life-span of dairy cows and its economic significance. II. The replacement of dairy cows: an economic model (author's transl)].

A model, initially based on the work of Zeddies (10), is presented , by which the economic aspects of the replacement problem may be studied. First, the principle underlying the replacement decision is discussed. Then, the data to be included in the model are determined. This mainly concerns the elements associated with age, such as milk production, the value of newborn calves, the slaughter of the cows, the feed cost and the cost of a pregnant heifer just before calving. The age-associated probability of culling is also included in the model. A number of questions regarding the economic importance of the duration of herd life have been studied using this model. In the third paper, the results of this application of the model will be presented.