Comparison of economically optimized culling recommendations and actual culling decisions of Finnish Ayrshire cows

Our purpose was to compare culling recommendations obtained from an economi c-optimization model with actual culling of Finnish Ayrshire cows. The dyna mic-programming (DP) model we used optimizes replacement and breeding decis ions to maximize the net revenues from cows currently in a herd and their p otential replacements over a 5-year decision horizon. Cows were described i n the model by five state variables: parity, stage of lactation. month of c alving, milk-production level, and days open (pregnancy status). We perform ed survival analysis to study the effects of those five factors on culling and to compare the actual culling of cows in December 1993 and June 1994 wi th the optimized replacement recommendations for the same months and for co ws in the same herds. The risk of culling increased as a cow grew older. both in the actual herds and in the DP recommendations for December. In the optimized replacements for June, however, the age of a cow did not play a significant role. A cow that had been in milk >270 days had a lower risk of culling than cows in ea rlier stages of lactation. When 305-day milk production increased by 100 kg , the risk of culling decreased by 4% in the actual herds and by 6 and 12% in the DP recommendations for June and December, respectively. When the day s open lengthened by a month, the risk of culling was 2.0- and 1.6-times hi gher in the actual herds and 1.7- and 2.0-times higher in the DP recommenda tions for June and December, respectively. Month of calving had a different effect in the optimized recommendations compared with the real-life situat ion: cows calving from January to August had a lower risk of culling than c ows calving in the fall in the actual herds, but the optimization model rec ommended heavier culling for cows calving between January and August. The DP did not account for diseases and did not allow replacements during t he first 2 months of lactation and some of the observed differences could b e due to this. However. the results suggested that Finnish farmers might no t be taking full advantage of the seasonality in milk pricing and productio n to maximize the profits of their herds - even though their culling decisi ons are rational and in quite close agreement with the optimized recommenda tions. (C) 2001 Elsevier Science B.V. Ail rights reserved.