DYNAMIC PROBABILISTIC SIMULATION OF DAIRY-HERD MANAGEMENT-PRACTICES .2. COMPARISON OF STRATEGIES IN ORDER TO CHANGE A HERDS CALVING PATTERN

A dynamic probabilistic simulation model is further extended and used for a comparison of different strategies in order to change the calvin g pattern of a herd. The Markov chain approach is used to simulate her d dynamics. Strategies to change the calving pattern focusing on the f arm's intake of replacement heifers, allowing a certain variation in a ge at first calving, are compared. A method has been developed which a llows the tuning of the available replacement heifers to the desired h eifer calving pattern, using linear programming. In the basic analysis a spring calving herd is changed into an autumn calving herd. The dif ference in gross margin per cow per year between the starting and the desired situation is Dfl. 115. The strategy that allows the largest va riation in age at calving is fastest in changing the calving pattern. It takes 9 years to realise the desired herd calving pattern, while th e desired heifer calving pattern is reached after 2 years. This strate gy is also the most profitable one. When considering a period of 10 ye ars, this strategy on average yields Dfl. 105 per cow per year. For a strategy that does not allow changes in the initial age at calving, th e increase is only Dfl. 6 per cow per year after 10 years, while in th e previous years the costs of changing exceed even the benefits. An ad ditional measure which does not allow cows to be inseminated in certai n months during the first few years, shows not to be economically attr active.