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The objective of this study was to estimate the economic impact of subclinical ketosis (SCK) in dairy cows. This metabolic disorder occurs in the period around calving and is associated with an increased risk of other diseases. Therefore, SCK affects farm productivity and profitability. Estimating the economic impact of SCK may make farmers more aware of this problem, and can improve their decision-making regarding interventions to reduce SCK. We developed a dynamic stochastic simulation model that enables estimating the economic impact of SCK and related diseases (i.e. mastitis, metritis, displaced abomasum, lameness and clinical ketosis) occurring during the first 30 days after calving. This model, which was applied to a typical Dutch dairy herd, groups cows according to their parity (1 to 5+), and simulates the dynamics of SCK and related diseases, and milk production per cow during one lactation. The economic impact of SCK and related diseases resulted from a reduced milk production, discarded milk, treatment costs, costs from a prolonged calving interval and removal (culling or dying) of cows. The total costs of SCK were €130 per case per year, with a range between €39 and €348 (5 to 95 percentiles). The total costs of SCK per case per year, moreover, increased from €83 per year in parity 1 to €175 in parity 3. Most cows with SCK, however, had SCK only (61%), and costs were €58 per case per year. Total costs of SCK per case per year resulted for 36% from a prolonged calving interval, 24% from reduced milk production, 19% from treatment, 14% from discarded milk and 6% from removal. Results of the sensitivity analysis showed that the disease incidence, removal risk, relations of SCK with other diseases and prices of milk resulted in a high variation of costs of SCK. The costs of SCK, therefore, might differ per farm because of farm-specific circumstances. Improving data collection on the incidence of SCK and related diseases, and on consequences of diseases can further improve economic estimations.
SloanFoundation and the second held a National Science Foundation Senior Postdoctoral Fellowship. While at the Institute, the authors had the benefit of inspiring conversations with A. Borel, D.l\1ontgomery, and J. P. Serre. Announcements of some of the results were made in the Bulletin of the American Mathematical Society [24] and [25].The present version was completed during the summer of 1970 after a one year special program in category theory at Tulane University with visits by S. Mac-Lane and many others. Even before that occasion S. MacLane had taken an interest in our work and had contributed valuable advice. The Chapter on Kan e:ll.-tensions, which reflects considerations not available two years ago, is typical of the new material added.Correspondence with L. Evens and S. Priddy contributed to our understanding of the cohomology ring of a finite group and certain resolutions. Concerning the computation of the cohomology of a classifying space, we had important conversations with A. E. Dold and D. Puppe, who also contributed remarks about the singular cohomology of K (n, n) spaces. During the summer of 1970 the authors were supported by the National Science Foundation.It is a pleasure to acknowledge the cooperation of Eric Nummela who accepted our invitation to write Chapter VI and to contribute to our discussion the insights he had obtained in his dissertation about classifying spaces for compact monoids. He also contributed to Section 2 of Chapter III.
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