Optimizing replacement decisions for Finnish dairy herds

The purposes of the study were to determine how "an optimal herd" would be structured with respect to its calvin:: pattern, average herdlife and calvi ng interval, and to evaluate how sensitive the optimal solution was to chan ges in input prices, which reflected the situation in Finland in 1998. The study used Finnish input values in an optimization model developed for dair y cow insemination and replacement decisions. The objective of the optimiza tion model was to maximize the expected net present value from present and replacement cows over a given decision horizon. In the optimal solution, th e average net revenues per cow were highest in December and lowest in July, due to seasonal milk: pricing. Based on the expected net present value of a replacement heifer over the decision horizon, calving in September was op timal. In the optimal solution, an average calving interval was 363 days an d average herdlife after first calving was 48.2 months (i.e., approximately 4 complete lactations). However, there was a marked seasonal variation in the length of a calving interval tit being longest in spring and early summ er) that can be explained bg the goal of having more cows calving in the fa ll. This, in turn, was due to seasonal milk pricing and higher production i n the fall. In the optimal solution, total replacement percentage was 26, w ith the highest Frequency of voluntary culling occurring at the end of the year. Seasonal patterns in calving and replacement frequencies by calendar month and variation in carving interval length or herdlife did not change m eaningfully (<1%-2%) change in the output variables) with changes in calf, carcass or feed prices. When the price of a replacement heifer decreased av erage herdlife was shorter and replacement percentage increased. When the p rice increased the effect was the opposite.